Sorry to resurrect an old thread :-). I test drove a used 2009 e90 dct m3 yesterday...first m3 I've driven.. Noticed a very odd sound, only when accelerating under load. Sounded like crackling/fluttering, almost like air trapped under paper. Seemed like it was more from the front left of the vehicle. I wouldn't say it was a "rattle" as some have described, but more a crackle, or sound like tearing something. Very weird.
I will obviously bring it up when I get the PPI, but just wanted your input as to whether this is the same kind of noise so many are hearing during acceleration. I parked the car and revved the engine, and the sound wasn't there. Only during acceleration was it there. I should've paid attention to e rev range when it happened, but unfortunately I didn't. Car seemed great other an that, and other than the driver side mirror not lining up properly.
Thx for any help! Hopefully will be an m3 owner by the end of January :-)