I used to have an issue with my M3 and X5. After some research it seems that BMW had these issues a LONG time ago and after much research on their part, figured out the proper combination brake pad compound and rotor alloy to avoid it. After trying many many diff combination...I went stock rotors and pads from the BMW dealer....no more issues on either cars.

__________________
97 E36 M3 SC with 420 WHP (my fav)
02 E53 X5 4.4
08 Cayenne Turbo