buzz at 2k rpm?

[ryguy0492]

Hey guys, I have an 08 6mt coupe. Pretty good shape overall, I've noticed I get a buzz right at 2k rpm while driving, been trying to find the cause.

It will buzz either on or off the gas, as soon as I touch the 2k rpm area. It's really only noticeable with the windows up but it's pretty loud.

I've been under the car both with a lift and underneath in a pit, with my mechanic, pulling and trying to move pieces, nothing seems loose. Exhaust hangers at the diff look great, exhaust itself isn't too wobbly.

The muffler was broken at the rear-most hanger, was one of the first things I noticed when i got the car and I threw some welds at it. Maybe I should cut it back off?

Anywho... thanks for reading, throw any buzzing advice at me

[ryguy0492]

any ideas?

[sgreer78]

When I did my x pipe, the clamps at the back before the axle were twisted up enough to just touch the metal heat shield and would buzz at a certain rpm, usually during cold start. easy fix, maybe yours could be the same.

[ryguy0492]

thanks sgreer, I'll check that, though I have an oem x-pipe but my muffler was ACM bypass modded

[Styral]

I had a similar issue, it ended up being the brace that holds up the x-pipe. I had to get the two bolts alot tighter than I originally thought.

[ryguy0492]

thanks, I will definitely check that tomorrow too. 1 degree currently in NY!

My car is also your twin styral, 08 alpine 6mt coupe

[pbonsalb]

How are the motor mounts?

[ryguy0492]

no idea! how could I tell? It does seem like the engine "moves" a bit in there.. like from idle, revving it up from 600rpm doesn't feel too "tight"

[Redd]

2k rpm is almost always exhaust resonance. But the resonance can send vibrations anywhere, even inside the cabin. I'd get under the car and give the entire exhaust - front to back - a good knocking with your hands and see where it's touching the body when it moves.

[Mvy]

+1 on the heat shield. I bet your cats are touching it and buzzing on cold start. It so tight in there that its easy for things to touch after messing with the exhaust. Since you had a broken hanger further down the line, it might have shifted the exhaust parts closer to the motor around a bit.

[ryguy0492]

thanks mvy, I will check down there again near the cats, everything seems pretty tight but it's possible I missed something. I managed to turn the bolts holding the center exhaust support (the rectangle piece) a half a turn each or so until they were really snug. That didn't solve my buzz really at all

I do think the rear section hanger was broken for a long time, but i rewelded it to the stock point a while ago and recently went and snugged all the hanger bolts

[Mvy]

My cats were too tight, and touched the heat shield and buzzed. Once they warmed up , or i hit the brakes hard, it stopped. We hammered the heat shield with a flat iron and mallet to push it away and got it pretty quiet now, but not completely every time. It goes away after Im warmed up. I deleted cold start and that helped a lot.

For me the buzzing was a combo of factors , HFCs(little footballs in shape) vs stock cats(pancake shaped), and because I didn't change my motor mounts before doing the exhaust. Once I did do them, it changed the measurements on the exhaust by half an inch! So word to the wise, change mounts when you intend to install a new exhaust (assuming the car is of age for the mounts which is 30k or 3 years on most cars)

[ryguy0492]

you really think motor mounts are needed that frequently on cars? Do you think worn motor mounts on our cars could cause a double, solid "knock knock" from the car as I leave 1st gear? Like say I'm sitting at a stoplight, as soon as I find the bite point with the clutch, the moment I move I get a solid "cluck, cluck" from somewhere under the car. It's almost always exactly those two clunks, never more. Never hear it while driving and such, only when leaving 1st gear, or when making slow turns into a driveway

Any way I could tell if my motor mounts are bad by looking at them? Get under the car?

thanks in advance

[Mvy]

These cars are known to go through mounts fast. See https://www.m3post.com/forums/showthread.php?t=1418410 and https://www.m3post.com/forums/showthread.php?t=1005111. I got the 30k mileage from others who have been better at staying on top of them than I was. I didnt change mine until late 60k and as I said, it made the entire motor sag a half an inch and I could feel every movement. I got some banging when taking the car over bumps at high speed that went away when changed. It really helped 6mt shifting and made it feel more precise changing the motor mounts. Id just plan to change them soon if you dont have evidence it was done based on the age of the car. Its well past due.

The clunk you are noting is prob not the mounts but the drive shaft/center support bearing. Its known to clunk and in most cases its normal and not a big deal is the consensus.
https://www.m3post.com/forums/showth...ighlight=clunk

[ryguy0492]

thanks a ton man..