rattling noise during 1st gear

Originally Posted by sean77693

2009 370 z M6

Dont listen to anyone if they tell you that this noise is normal...if youre anything like me when it comes to my toys im exceptionally "OCD" shall we say about anything that feels or sounds like it could be a problem. That being said, ive looked into this noise because my car just recently started making it, but ive heard other cars throughout my life make the same noise, so it wouldnt be a manufacturer spec. problem. Then i YouTubed any videos i could find to see if i could hear a replication of the noise. After a few hours and some research, along with my auto tech history and knowledge i came to my own conclusion, which is....

Because the sound is only at low RPMs
always taking off from a slow or dead stop
goes away when the car is up to speed and rpms are up
and seems to only happen when the clutch is engaged (pedal NOT pressed)
i believe that the problem comes from and input shaft bearing or a pilot bearing, when these wear and there is play it will cause the clutch to engage with the pressure plate not quite exactly dead center this makes a harmonic vibration or a chatter noise that is amplified by the bell houseing of the transmission. When the Rpms rise the clutch disc spins faster causing centrifugal force to align the clutch and pressure plate and balance the shaft. Thus no more vibration, and no more noise. All that said the bearing isnt really going to cause any mechanical problems, at least initially however, if the wear becomes too excessive i suppose it could cause alignment issues in the transmission... but personally i cant stand the rattle so for peace of mind i just think ill replace all bearings, may as well they are cheap and if it needs to be taken apart for one might as well get ahead on preventative maint... ill follow up after the service to confirm or feel stupid and apologize..

NOT to be confused with a throwout bearing.....pilot/input bearing.

I could be wrong but from what ive seen, read, and experienced this is my theory.
https://youtu.be/nWWi74xKt8A