Strange NVH in deceleration with different gears

[jvictormp]

Hi guys

I have a 2008 E92 6MT M3.

Since I've got this car, two years ago, there is a strange NVH that shows up when I let the throttle off with RPM above 4000RPM or so.

I could describe the sound like a cellphone continuously vibra-calling in the boot (but loud enough for the occupants to hear inside the cabin).

The sound get lower as the RPMs decrease.

Happens in 4th or 6th gear. Very rare in the other gears (maybe I never heard it, can't remember).

Doesn't happen everytime.

When it happens, if I push down the clutch completely and leave it again, the sound sometimes doesn't appear again. Sometimes it does.

7 months ago, I changed the rod bearings and the engine mounts (these were dead, one of them separated the rubber from the metal part, I put the Corteco ones). The following days seemed like the noise never happened again.

But after approximately 4 months and 700 miles I began to hear it again, so I guess it's not related to engine mounts and maybe it was never solved.

I know I have a pinion diff seal leaking, and the new seal is ready to be installed, but I guess the NVH doesn't sound like a diff problem.

Anyway I feel like I should check the drive shaft center support bearing, but doesn't have much hope on that.

May I have a problem with the gearbox or the clutch?

EDIT: it's relevant to say that wheel hops are veeery frequent on this car. I'm even thinking on changing the rear subframe bushings for solid ones. But I think this could be related to the noise, because the wheel hop happen too often.

[Redd]

If it only happens when you let the throttle off and it's coming from the boot area, it might be exhaust related. Check your exhaust mounts and heatshields to see if they are rubbing. What exhaust are you running?

[pbonsalb]

Could also be driveshaft (transmitting diff noise or its own noise if there is a u-joint or spline joint issue)or clutch/flywheel related (transmitting transmission noise).

[roastbeef]

sounds like a driveline problem.

[jvictormp]

Originally Posted by Redd

If it only happens when you let the throttle off and it's coming from the boot area, it might be exhaust related. Check your exhaust mounts and heatshields to see if they are rubbing. What exhaust are you running?

OEM Mod.

Actually two weeks ago I found a manifold heatshield (that one bolted to the engine headers) loosen, only one bolt holding it.

I put the other two bolts and fixed it. But the NVH didn't change at all.

[jvictormp]

Originally Posted by pbonsalb

Could also be driveshaft (transmitting diff noise or its own noise if there is a u-joint or spline joint issue)or clutch/flywheel related (transmitting transmission noise).

Originally Posted by roastbeef

sounds like a driveline problem.

Yeah, that's what I suspect of.

If it were driveshaft, I think NVH would increase and decrease only related to wheel speed, independent of engine RPM.

But no, it's related to engine RPM, which makes me think it's a transmission problem, and that scares the hell out of me.

[Redd]

Can you take a video of this sound? Preferably from inside the car and outside (if you can somehow mount a Gopro under the car).

[jvictormp]

Originally Posted by Redd

Can you take a video of this sound? Preferably from inside the car and outside (if you can somehow mount a Gopro under the car).

Ok, I'll try that, but I'll only be home in 20 days.

[jvictormp]

Could it be transmission mount? Car's got 42000 miles.

[Redd]

Originally Posted by jvictormp

Could it be transmission mount? Car's got 42000 miles.

Transmission mounts almost never fail.

[SkiFly01]

I'd look at items along the driveline, such as motor mounts, guibo, center support bearing, diff mounts, and even sub frame mounts.

[jvictormp]

Yeah, I'd like to change them all, but for multiple reasons I need to take a sure shot, so I'm going by the its variation with RPM, so it needs to be before the gearbox.

If it's not gearbox mounts, I'm thinking it's flywheel/clutch problem.

There is some strange noise too when engine is idling and clutch is engaged, neutral gear. If I push the clutch pedal and pull off again, the noise goes away. Sometimes the noise doesn't even show up. But it's very common it shows.

Didn't mention that in the beginning, because for some reason I assumed that it is common to every manual M3. Now I figured that I should ask if it really is.

[Ab28]

Originally Posted by jvictormp

Could it be transmission mount? Car's got 42000 miles.

Originally Posted by Redd

Transmission mounts almost never fail.

It's true. Mine at 111,000 looked almost new.

[patroklai]

OP did you ever figure this out? I have a faint "thud" when I let off the gas above 4k rpm or so. The lower the RPM the less noticeable or unnoticeable it becomes. Higher RPM, let go of gas. THUD! Feels like the clutch is catching or something of the like. I have solid race motor mounts (turner ones IIRC), 90-95a durometer trans mounts (I think, it's been a while), fresh guibo from a few years ago along with support bearing.

My sense tells me it's coming from the clutch area.

[jvictormp]

No, I did not. I can only suspect of clutch too, but I'm just letting go right now.

[jvictormp]

Updating.

My flywheel was missing the pilot bearing. That was the cause of the NVH. Now the bearing is there, and the NVH is gone.