I have less than 50 miles on the car and have a loud and somewhat disconcerning noise coming from the brakes that gets louder as the car slows. It sounds like a jet engine or turbine throttling down. I did some quick research and found this thread from our M3/M4 brethern with the same issue:
http://f80.bimmerpost.com/forums/sho....php?t=1033297
The sound is perfectly portrayed in the video in the second post of that thread around the 6:15-6:25 timeframe. I think it is caused by the pattern on the surface of the brake rotors, as seen in this picture:
http://f87.bimmerpost.com/goodiesfor...80_highRes.jpg
Apparently this sound goes away as you drive the car more and more, but to be safe, I am ensuring the brakes are bedded in properly. If you need tips on how to bed brakes tire rack has a few recommendations:
http://www.tirerack.com/brakes/tech/....jsp?techid=85