Intake noise?

[DonMarcoPolo]

I recently got a '95 L BD, and I've noticed a strange sound while I'm driving around that has me pretty well stumped. It only happens under WOT, and is not directly related to engine RPM. The sound (which sounds like a high-pitched hiss) starts about the 3k range, and has a single-distinct tone. At about 5k-6k, the tone changes to a higher, louder hiss. I emphasize that there are only 2 different noises I hear, they don't get any louder as the rpms increase. This is the same all the way through the gears. People often ask me if its my turbo, and when I say I don't have one, everyone seems to want to ask me if I'm sure. I'm POSITIVE I don't have a turbo, as I'm sure everyone here knows.

Anybody ever heard of this sound?

[Huffer]

Could be an exhaust leak.

[GTDrifter]

i dont wanna post steal but i have a question about a sound my car and my friend's makes

its like a chirping sorta sound happens alot if i push the rpm to 5 and then let it shift

any thoughts on what it is?

[gryffinwings]

Could be an exhaust leak.

+1, definitely an exhaust leak, I heard the same thing from someones Toyota Celica, and he knew he had the same thing.

[DonMarcoPolo]

Not discrediting anybody, but if somebody could explain how it would be an exhaust leak (heard from the engine compartment, and not hearing an exaggerated note from the engine), please do, because that makes no sense to me. Any time I've heard an exhaust leak from anybody's rig, its always been a slightly lesser version of what it would be like if they had just been running around with open headers...then again, I only know American, so I know there are lots of things that I don't know/understand.

~Mark

[xXGTBspecXx]

if you have a intake it could be a very restrictive air filter(they whistle)or new airbox filter(if stock) or it actually could be a small vacuum leak(it happens)

[Huffer]

Not discrediting anybody, but if somebody could explain how it would be an exhaust leak (heard from the engine compartment, and not hearing an exaggerated note from the engine), please do, because that makes no sense to me. Any time I've heard an exhaust leak from anybody's rig, its always been a slightly lesser version of what it would be like if they had just been running around with open headers...then again, I only know American, so I know there are lots of things that I don't know/understand.

~Mark

Well your description is hard to pinpoint - when you describe a SOUND, you're relying totally on the other person's interpretation of the description.

But, the firewalls and sound insulation on these cars isn't all that great (but better than a same-year Impreza) so you actually can here a number of engine related sounds from inside the cabin.

In the end though, we're all just guessing based off your description.

[Grafton]

i believe that i have had the same sound, does it happen if you rev it up in netural, what about as your driving along reguardless of what gear and where you are in the power band and punch it it ?

if so it was my alternator, had a squeak in it as it turned.
found it (the sound) while i had it off and was turning the pulley slowly an heard the squeak

also check the positive terminal if you need to replace the alternator the one on my new terminal was too big for the stock ring terminal.

[Drakien]

Just a guess, because I have a similar sound(I dont know if I would call it a problem) but on the back right side of the intake manifold is some sort of Pressure Release Valve(I think). Its kinda hard to see in this pic, but its the only pic I could find right now and its dark outside. Mine doesnt start releasing pressure until about 5k RPM's. And if I am accelerating strong and shift roughly at 5k RPM's I get a nice sounding PSSSHHHH. Its not really loud, but you can hear it. But I have a 2.5l so it might be different if you have the smaller engine.

https://sl-i.net/FORUM/images/imported/2008/09/333640568-1.jpg

(this is not my engine bay, This is just a picture I found on google to help explain my theory)

[Grafton]

yeah the vacuum system and throttle body are a little different between the 2.2 and the 2.5

[DonMarcoPolo]

Hmm...anyway I can check for those things while I'm under the hood? As far as I've been able to tell, I haven't been able to duplicate the sound in neutral...It only ever does it when I'm actuallyl driving.

[Huffer]

It could be a normal induction sound... I took out all my airflow silencers and when my car goes WOT the intake screams and the exhaust is loud.
I do have an STI cat-to-axleback though.

[DonMarcoPolo]

It could be a normal induction sound... I took out all my airflow silencers and when my car goes WOT the intake screams and the exhaust is loud.
I do have an STI cat-to-axleback though.

What airflow silencers? Also, what is a snorkusectomy?

[99SUS SFD]

A snorkusectomy is when you take the intake silencer off of the intake that's located in the passenger-side fender. Do a quick search and you'll see some different topics about it...including how to's.

[DonMarcoPolo]

A snorkusectomy is when you take the intake silencer off of the intake that's located in the passenger-side fender. Do a quick search and you'll see some different topics about it...including how to's.

Wow, thats some awesome info...just spent about an hour bouncing from thread to thread to thread...gonna take care of that first thing in the morning :grin: Thanks.


~Mark

[99SUS SFD]

It's a pretty quick process. Make sure you take out the wheel liner entirely. You'll be surprised how big that thing is.

[DonMarcoPolo]

Wow, I just finished about 30 minutes ago (had to take care of some stuff before hittin the comp), and yes, delightfully easy. And HORRIFIC how much junk was hidden in the fender...yikes. Drove it around for just a little bit...man, that sounds so much more aggressive! Can't wait to get my exhaust all done up.

In other news, getting back to my original post, I pinpointed about the rpms of the sounds...instead of what I had originally posted, the sound starts at about 3k @ WOT, and changes at about 4250 to the higher pitch. been tryin really hard to hear it in the engine bay (using the throttle linkage instead of the pedal), and I'm about ready to just say screw it and call it fine.

[Huffer]

I pinpointed about the rpms of the sounds...instead of what I had originally posted, the sound starts at about 3k @ WOT, and changes at about 4250 to the higher pitch. been tryin really hard to hear it in the engine bay (using the throttle linkage instead of the pedal), and I'm about ready to just say screw it and call it fine.

It could be just wind as you are driving... if you can't hear it in the cabin while the car is stationary and you're just increasing RPMs...

[DonMarcoPolo]

It could be just wind as you are driving... if you can't hear it in the cabin while the car is stationary and you're just increasing RPMs...

I discovered today that I actually can hear it a little when I'm stationary and go WOT, but once I get under the hood, I have no way of knowing where the heck its coming from :mad: I put my head right by the alternator and gassed it (nothing). Went to the back of the engine bay and gassed it (nothing)...seriously WTF ?! something this pronounced would be recognized by everybody with the same car as mine, so something HAS to be wrong...so frustrating...I like this car and have lots of plans for it, but I hate to think I have a problem (big or small) that could be getting worse evertime I drive it.

[DonMarcoPolo]

also, it is definitely a loud noise...anytime I pass something (e.g. buildings, other cars, a shrubbery), I hear the sound of my car taunting me with its mystery sound :?: Yesterday when I left work, my boss told me he heard it as I was driving away...again...WTF?!

[98BG5GT]

I would agree with all of Huffer's suggestions. It would be difficult for anyone here to guess the source of the noise. It's all subjective to us. It may be normal just because of wear and tear to pulleys on your belt drives, or vacuum related leaks that do not largely affect the handling of your car. Sounds from the inside of the car cabin are entirely different than what you hear outside because of the physics of high and low frequency sound waves. It could also be the fuel pump under your rear seat. Who knows? My guess is that since you tend to drive at WOT wide open throttle, this would suggest at WOT the butterfly valve opens up horizontally exposing the butterfly edge towards surging incoming intake air resulting in a turbulent "whistle effect" characteristically described to the whine of a turbocharger. At WOT, this would also suggest a large volume of air channeling through the intake manifolds and plenum resulting in turbulence. The rough edges and mating surfaces on the inside of the throttle assembly, manifold and head are usually not ported and polished fom the factory resulting in rough turbulent edges which can also contribute to high pitch hissing noises in the engine compartment.

[DonMarcoPolo]

is there any relatively easy way to check and see if it is a belt/pulley?

[DonMarcoPolo]

i believe that i have had the same sound, does it happen if you rev it up in netural, what about as your driving along reguardless of what gear and where you are in the power band and punch it it ?

if so it was my alternator, had a squeak in it as it turned.
found it (the sound) while i had it off and was turning the pulley slowly an heard the squeak

also check the positive terminal if you need to replace the alternator the one on my new terminal was too big for the stock ring terminal.


How about that. Feel free to say "I told you so". Yesterday, I smelled something like burning wires but couldn't find anything, and last night, my BATT light came on. Took the alternator off and got it tested...FAIL!! . . .F**K! :banghead:

I've been all over town checking price/availability...damn, these things are expensive! of the 2 salvage yards in town, 1 isn't open on the weekends (WTF?) and the other has a 1st gen with NO ALTERNATOR!! . . . Grafton, I shoulda been all over your advice...shame on me :oops:

[DonMarcoPolo]

Ok, I think I'm just gonna stop posting on this one, cuz once again...its still a mystery...I just finished replacing the alternator ($160), and the sound is still there. The fact is that the alternator WAS actually bad, so its not all a bad situation, but its starting to remind me of some sort of looney-toon episode where somebody winds up blowing a whole building to hell trying to get some irritating little critter, and amongst the rubble is a perfectly untouched spot with the little critter just sitting there continuing to annoy the guy.

(sorry to rant for so long on this topic)

SOunds like an issue I've been having. I can hear the noise inside the car, and outside the car. it happens when the car is idling, and when im driving. seems to go away for a split second when im accelerating and then comes back. My mechanic checked for vacuum leaks and said he could not find one. SOOO, my next guess would be exhaust maybe? I can also smell exhaust inside the cabin when i accelerate, especially if the windows are open.

[ProjectLGT97]

I have the same exact problem!!! Changes pitch at the same RPMs and everything. I've been going nuts trying to figure out what it is. I was thinking maybe its the rear diff since it only happens under load and when you are really torquing the engine/trans

[DonMarcoPolo]

YAAAAAAAY!! I'm not the only one!! Sometime soon, I'm just planning on takin' the engine apart (to clean and polish everything I can), then put it all back together with new seals/gaskets...while I'm at it, I'm gonna see if I can find/get rid of it...sooner or later, SOMEBODY is bound to figure out WTF this is.

[ProjectLGT97]

Well i will tell you.. I just blew my motor racing and I just put a new motor into my legacy and the high pitched hiss was there with the old engine and its still here with the new engine. I could see how you could think the hiss was from the front because that's where i thought it was initially however my dad sat in the back of the car while i drove and seemed to hear it behind him. Thats why i'm tempted to believe it has something to do with the rear diff...

[DonMarcoPolo]

hmm...so, so strange.

Sounds to me like something is going out...possibly the a/c compressor or maybe one of the pumps ie power steering, or maybe even the alternator.

[ProjectLGT97]

Sounds to me like something is going out...possibly the a/c compressor or maybe one of the pumps ie power steering, or maybe even the alternator.

I would run with your theory however, the car only does it in gear and the pedal must be depressed more then halfway for the noise to come.

[1-3-2-4]

Mine did the same with an Ebay blue cone filter.. I think I might have a video with my impreza doing that.. as you say it happens around 3K but falls off sharp after that.

All I did was take out snorkus and left stock tubing.

I replaced my air filter with just another regular Fram air filter....the air filter box is tight as far as I can tell, so I'm fairly certain that the noise isnt coming from there.

[98BG5GT]

My guess is that since you tend to drive at WOT wide open throttle, this would suggest at WOT the butterfly valve opens up horizontally exposing the butterfly edge towards surging incoming intake air resulting in a turbulent resonance characteristically described to the whine of a turbocharger. At WOT, this would also suggest a large volume of air channeling through the intake manifolds and plenum resulting in turbulence. The rough edges and mating surfaces on the inside of the throttle assembly, manifold and head are not smooth from the factory resulting in rough turbulent edges which can also contribute to high pitch hissing noises in the engine compartment. Also, the rear differential should not make any noise if your car is revving while stationary.

I dont drive at wot.

[1-3-2-4]

Mine did not have a whine but more like the sound of pressure building you know the sound of the air being sucked in.

[ProjectLGT97]

It happens anywhere between the pedal halfway depressed and WOT. And the pitch doesn't die at 3k it merely changes to an even higher pitch once it hits 5k

[98BG5GT]

I replaced my air filter with just another regular Fram air filter....the air filter box is tight as far as I can tell, so I'm fairly certain that the noise isnt coming from there.

Was this "noise" present since you owned the car? Can you record the "noise" you are referring to? Post it to this thread. It might give us an idea of it's origin.

Yeah, its been there since we bought the car. I will have to get my cell phone and see if I can record the noise and put it up on here.

[1-3-2-4]

crap I had the sound on my Minidisc recorder meant to bring the file with me to work.

It was hard to capture the sound but then again back then I had a crappy PC mic.

[1-3-2-4]

Finally posted the file lol

http://media.putfile.com/hissing-cone-filter

[ScaryFatKidGT]

just a random thought im probably wrong but could it be something the ECU does at 3k and 4250? does it change something with the air and fuel?

like ramp up the injectors and fuel pump and make a hiss? or something

[joshjosh619]

It could be a normal induction sound... I took out all my airflow silencers and when my car goes WOT the intake screams and the exhaust is loud.
I do have an STI cat-to-axleback though.

How do i remove the airflow silencers? sounds like it would be awesome and provide better airflow to the engine.

[joshjosh619]

i also have the same noise and enjoy it. i wish it was louder actually.

[WinterKnoll]

I'm not sure I really understand exactly what the noise is that is being described, but I've had a noise that sounds like it fits the description pretty much ever since I bought the car.

[Huffer]

Finally posted the file lol

http://media.putfile.com/hissing-cone-filter

Sounds normal, pretty bad recording though.

[1-3-2-4]

well I had to take the bass out for one so it could be heard better and other is it was a computer mic in the engine bay I could make it clip real easy... I have a way better mic now...