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I could use a little help with this. I've searched the Bimmer boards, though have not come up with any leads. My car is making an unknown noise. No one can seem to diagnose it. I have heard it on other ///M's, that's what's throwing me. The car is tight, pulls like hell and the clutch is fine. The noise is most relevant when up-shifting and decelerating in 2nd, 3rd and 4th gear. I can only best compare the noise to a rattle snake. i.e., when up-shifting the noise would occur when the clutch is disengaged, also when decelerating it occurs as soon as I lift my foot from the throttle in certain rpm ranges. I work for a Bimmer dealer and have had my tech friend listen to, just to say it's nothing to worry about. My instructor at my last Auto-X works for ZF and he didn't seem to think it was the gear box. I'm at a loss. What, if anything can I do beyond what I've done to diagnose this?
Thanks- :mad:

I'm guessing you are having a hard time determining exactly where this unknown noise is coming from...engine, transmission, exhaust, etc.

It could be the VANOS or it could be the interior section of the catalytic converter has broken its welds which causes it to rattle when it doesn't have ample exhaust pressure to keep it from moving inside the housing.


Bob ///M3

I can say for sure it is NOT the vanos or either tensioner. I replaced those. I guess I forgot to mention the noise seems to be coming from underneath the car, mid section.

How about the CAT then?

Bob ///M3

I would check your flywheel....I have had similar symptoms and it was my flywheel (it needed to be resurfaced)...I know it's hard to believe but it's true...

Bob
Did you read the below post about the flywheel? What would occur to make a flywheel emanate this sound? Could be my CAT, I was going to swap in a straight section in a week or so. I guess I would know for sure then.
widebodym3, when you had the flywheel resurfaced did they say what the cause was. Also, how did you - they - come to the determination that's what it was?

I can't say that I've ever heard of a flywheel making the kind of noise you describe when "up-shifting and decelerating in 2nd, 3rd and 4th gear".

I know the sound it makes when the clutch slips, or the flywheel has been overheated and/or warped...or when a lightweight flywheel has been installed but it doesn't coincide with your discription...

Bob ///M3

PS - Lets move this thread over to the "Help For Mechanical & Maintenance Questions" forum and see if you get any more input.


Originally posted by ///M-COZMIC
Bob
Did you read the below post about the flywheel? What would occur to make a flywheel emanate this sound? Could be my CAT, I was going to swap in a straight section in a week or so. I guess I would know for sure then.
widebodym3, when you had the flywheel resurfaced did they say what the cause was. Also, how did you - they - come to the determination that's what it was?

Also, I wasn't aware you could resurface a dual mass flywheel. I thought that was a no no.
Guibo? What would this emanate if faulty???

Originally posted by ///M-COZMIC
Also, I wasn't aware you could resurface a dual mass flywheel. I thought that was a no no.
Guibo? What would this emanate if faulty???

Shit...I made a mistake...You are right..I had the flywheel replaced (it was so long ago..that I couldn't remember)...Also the symptoms I had were a liitle different (I just called my mechanic to confirm) I had a bad rattling sound at idle (w\o clutch engaged) as soon as I engaged the car into gear the noise went away...Sorry for the confusion

BTW: A guibo issue will have vibration in the shifter...