Name this sound.

[PhilPhil]

Okay, I have a funny sound my Z3 M Coupe (model year 2000 S52) is making. I'll describe it in detail. But first, I should mention that the car has 56k miles on it, and is it fairly pristine shape. Vanos has been done, and has no leaks of any kind. Cooling system has also been recently updated. rear diff was rebuilt with Randy Forbes kit installed.

Sound description: It's a bit like the ringing of a school bell, or like dragging a piece of re-bar along the street. It tends to happen for less than a second at a time when slowly letting out the clutch from a stop. It's coming from the front of the car.

My first suspicion was the clutch, but it's only occasionally that it does it, and also it doesn't sound muted, like it would if it were inside the engine or transmission housing. It sounds like it's outside the engine, somewhere in the engine bay. This makes me think that, as the engine shudders a bit as the clutch is engaging, something is briefly rattling against something else. I looked at the front swaybar, but the only thing that's maybe within physical range of that is the underside of the engine/oil pan, and that's about 3/4" above. Maybe the exhaust? As I shut off the engine, parking in the garage, I did hear it give a little "ring a ding" just as the engine came to a stop. So, again, this seems like low frequency, high amplitude vibration that triggers it.

I only noticed it yesterday, and I plan on spending Saturday trying to figure it out. Have any of you heard anything like this? What should I look at first? Thanks in advance!

[Harvey Mushman]

climb under the car and start knocking on all the metal bits with a wrench. When you hear the *ping* of the same pitch as what you've heard while driving, then you know you've found it.

[MartyBtoo]

My first inclination is to check the motor mounts, to see if one of them is cracked enough to let the engine move enough that something hits as you let the clutch out.

Marty

[PhilPhil]

I'm really starting to think it's motor mounts. I was looking for DIY videos on YouTube and found one where the guy takes off the sort of bell-shaped heat shield off the passenger side motor mount. When he drops it on the ground, I thought that was the ringing sound I'm hearing. Maybe all I have to do is tighten the motor mount nuts? In any case, I have a new set of motor mounts and trans mounts coming, but I can't wait to check this out this weekend.

Here's the video at the spot where you hear the heat shield clang. https://youtu.be/7ytfXqPvauI?t=4m10s

Thanks for the tips, guys!

[e36 gang]

It could be a loose exhaust peice.

[BruceWarne]

Take a small wrench. Knock against the harmonic balancer. Same sound?
Took me hours under the car - and a new clutch, flywheel, release and pilot bearings - to diagnose mine.
In the end my wife found it, by listening while I pumped the clutch pedal.
Once she had the general area I started knocking on stuff, until “bling bling bling” same sound from harmonic balancer.
Engine stethoscope didn’t help, because of rubber isolation in damper.

In shop right now to get fixed.
Mine may still be something else, but I doubt it.

[PhilPhil]

UPDATE:

I watched a bunch of YouTube videos on vibration damper / harmonic balancer noises, and that's not the sound I'm hearing. My noise is exactly like a classroom bell ringing, but just for less than a second. Bright and, uuh "chimey", like a bell. Not so much a rattle.

Anyway, I spent a few hours under the car tapping things, and these are the things that sounded like possible candidates:
-Flywheel
-Drive shaft

At the same time, I replaced the motor mounts, wondering if they had deteriorated like every other part on this 18 year old car. The ones I swapped in are Bimmerworld performance/track mounts. Definitely more NVH than the OEM units. I may replace them next year with new OEM versions.

I also lowered the exhaust (at the rear, not the front) by about a half an inch. I though maybe it was finding something to ring against.

After the new motor mounts and exhaust adjustment, the sound was still there. Disappointed, I saw no choice but to drive the car 500 miles to ZFest in Missouri. The drive whent fine without issue. On the first day of ZFest, I heard the noise again, while parking, just like always. Over the course of the whole trip, I drove the car 1200 miles, often in a "spirited fashion". The car ran fine the whole time.

Here's the weird part. The frikkin' sound WENT AWAY. I never heard it after that first day of ZFest. Drove it home fine. After a year of hearing that intermittent and brief ringing sound while starting from a standstill, I haven't heard it since day one of ZFest. Bizarre.

Maybe it'll come back. I don't know. I guess I'll have to wait until it A) comes back, and B) gets persistent enough to where I can demonstrate it to my mechanic without him thinking I'm a car hypochondriac.

[PhilPhil]

UPDATE AGAIN: Okay, someone in the BMW M & Z3 Coupe Enthusiast group (https://www.facebook.com/groups/z3mc...6466239177630/) just posted a video of his Z3MC making the exact same noise. The overwhelming opinion is that it's the rear diff. I'll be watching this thread to see what the problem turns out to be, and what it costs.

[Cobra1956]

U joints on drive shaft?

[PhilPhil]

Adding that to the list of things to check. Thank you!

[Cobra1956]

It could be the brace also. The only reason I suggest that is while under the car if I hit or mess with the shaft the noise is a much high tone heading more towards the "bell" type. I have a dif on the bench now and from what I found wrong with it (broken bolts) it would be more catastrophic in my opinion if some thing was hitting. If you get under your car check all of the exhaust fittings for loose or damage areas.

Find Randy Mueller on the forums. He is a great mechanic and might be able to help you. Very analytical thinker.

[Cobra1956]

Phil, after re-reading this you might ask Randy Forbes specifically since he has so much knowledge and his kit was installed. Who did the install? Maybe something was not torqued properly and it has worked it's way loose. Dont know if you have access to this but in the past when trying to decide where noise was coming from I would get my car up to 40 mph and shut it off and let it roll (all safety precautions to not lock the steering) but it allowed me to eliminate parts of the car and hear better. There is actually not too much under there but you have to be patient and thorough while under there. I have a small lift so I get it it weekly after the track. Could even be debris between the rotor and a dust shield.

I had an annoying oil leak and Randy Forbes was able to point me to the fix in a few minutes where I had been dealing with it for a few years. Between the two Randy's there will be help. I would bet on that!

[catimann]

Do you have a mechanics stethoscope? that said my Exhaust is making a ringing type sound from the internals of the Cat I believe as the rear tail section is now different than stock and made no change. In the beginning it would ring for a time after start up and then go away as it warmed up.

Also can you get a better link to the video?