EJ22 Knocking noise

[mattjv89]

Hey everyone, hoping to get some ideas on this noise before I take apart anything major. 1999 30th anniv., 71k miles.

Two times over the past week I've heard a low knocking noise that sounds like it's coming from deep in the engine. It's not sharp or metallic sounding, much like lightly rapping your knuckles on a wooden table. I can only hear it at idle, it either stops or is drowned out when revving. Both times have been with the engine fully warmed up which leads me to think it's not the "piston slap" I've read about. The engine runs and accelerates smooth, and there is no CEL or other warning lights. My first (and worst) thought was a rod bearing but most of the videos I've seen of that have been a louder/sharper noise that remains noticeable with acceleration.

Any ideas? most of what I've read points to various valvetrain components but I'd love to narrow it down a little more before blindly tearing things apart.

[pleaidestar]

What kind of oil you been using or did you change viscosity recently? These motors do make a little more noise than traditional layouts. The motor in my car is running very well and its got some symphonic little noises to it.

A little more background on the motor and mileage could help, any past problems etc.

^i see 71k miles

[pleaidestar]

The valve train is on the outside of the motor and they are adjustable on your particular ej222, you got fairly low mileage considering the age of the vehicle but obviously never hurts to check them, but that's a pretty apparent ticking sound as your cams revolutions are quicker than the crank. Does the sound follow the revolutions the motor makes?

[mattjv89]

Always been using conventional 30 weight, the last change was about 500 miles ago and didn't correspond with the noise starting. There are no past issues I could see being related to this. I did check valve clearances about 5,000 miles ago when the covers were off to fix leaky spark plug well boots, found a few out of spec and corrected them. The sound does appear to follow the motor revolutions, though I can only hear it at idle. It also sounds "heavier" than what I'd expect a valve noise to be, closer to a thump than a knock.

[Wiscon_Mark]

If it's not valves, piston slap is the other "noise" that's common with Subarus.

[mattjv89]

Right, I've heard a lot about piston slap but I thought that was normally a cold issue and should stop as the engine warms? Every time this happens it's been at operating temperature.

[pleaidestar]

I hear knock sensors can create a knock if they are cracked