Grinding noise while decelerating in gear

[ecoflame]

The grinding noise is only heard while decelerating in gear. It's not dependent on vehicle speed only engine revolutions, usually above 2k. There's also a "grinding whooshing" noise while accelerating that's heard at 2.5k. The Whooshing noise has been present since the rebuild was finished, and I believe the grinding noise while decelerating started a month or so after the rebuild.

I have a lightweight flywheel and stage 1 clutch from exedy installed, I've read that some people have experienced similar noise after installing the same setups. I also have Group N motor mounts and pitch stop mounts installed.

Any ideas as to what is making the noise and how to stop it? Is it something I'm just going to have to live with?

The video below is the best I can provide at this point in time, sorry. :-(
http://youtu.be/kGew7S23ecA

[harrymaneuvers]

The grinding noise is common on a lot of subarus. It is mostly from upgraded bushings or lockdown kits in the driveline or rear diff/subrame but can also be caused by slight amount of lash in your diffs.

I just rebuilt my whole engine and put in a tranny and rear diff that only had 12k miles on them and even it does this. Basically when on the gas there is no sound... with the clutch pressed there is no sound... but anything above 2k RPM with the clutch out and the foot off the gas makes a metal on metal grinding sound that slows with the RPMs.

I have read quite a bit on this and it seems like if you dont have aftermarket bushings or lockdown kits then you might have a tranny crossmember or rear diff outrigger bolt that is loose, a missing bolt where the exhaust bolts to the tranny or possibly a bent rear diff outrigger mount plate as some people mistake this plate for the jacking point in the rear. If you do jack the rear up by this plate and bend/distort it at all, it will cause this grinding noise.

Basically it is just driveline vibrations resonating through two metal parts that are contacting eachother.


Like always though, I could be wrong.

[ecoflame]

See that's the general consensus from everything I've read too. But what bugs me is sometimes you don't hear it or maybe it's not as audible. Shouldn't it be a consistent noise and not waiver?

Even in the video it doesn't sound like it does in person. Maybe I'm just being overly paranoid since this is the first flat 4 I've worked on, but that noise scares/ annoys the crap out of me. It's even preventing me from moving on to getting the exhaust line installed because it bugs me so much. I'm on a tight budget right now and I don't want to start anything new if there's anything still not right from the rebuild.

[d1giPhux]

I had a strange grinding noise like this that for the LONGEST time bugged me. It ended up being a loose trans-crossmember bolt. Check yours. I tightened mine and my car was nearly SILENT after. It keeps coming loose too, so I have to keep tightening it. It would make a nasty metallic grinding sound when downshifting/decelerating.

Its worth a check. Hope your fix is as easy as mine was!

[harrymaneuvers]

Get the car up on Jackstands. Start from the front and work your way back checking all tranny crossmember bolts, rear diff bolts, motor mounts, tranny mount ect.

Then check the two plates on the rear diff outrigger and make sure they arent bent at all. If they are, then that is most likely your problem.

[ecoflame]

I had a strange grinding noise like this that for the LONGEST time bugged me. It ended up being a loose trans-crossmember bolt. Check yours. I tightened mine and my car was nearly SILENT after. It keeps coming loose too, so I have to keep tightening it. It would make a nasty metallic grinding sound when downshifting/decelerating.

Its worth a check. Hope your fix is as easy as mine was!

Yea I've actually read your ordeal, and I probably should check the tranny bolts. The only reason I haven't yet is because when I put everything back together I was very meticulous about tightening everything to factory torque specs. But if yours keep loosening themselves that might be what's happening to mine. I'll check mine today. Wish me luck that's what it is.


Get the car up on Jackstands. Start from the front and work your way back checking all tranny crossmember bolts, rear diff bolts, motor mounts, tranny mount ect.

Then check the two plates on the rear diff outrigger and make sure they arent bent at all. If they are, then that is most likely your problem.

That's basically what I'm about to do. Yay. :/

[Wiscon_Mark]

How about the bearings in the clutch assembly? When my pilot bearing went, I could have described it as a grinding noise under acceleration and definitely prominent under deceleration with the throttle closed too.