Originally Posted by eatrach73
bearings don't make that kind of noise.
OP i want to ask you, is the noise same on the right and the left; meaning, if you closed the right window, and opened the left, is the noise identical?
NOw that i heard D47m122, I think it is the exhaust hangers??? maybe??
NO, the sound is from pebbles stuck between the brake heat shield and rotors. This is a FACT. This happened to another M3 as well as mine during a recent BMWCCA car control clinic. The parking lot had a lot of loose gravel.
The reason the sound sometimes goes away for a day or 2 and then comes back is because the pebble gets stuck (possibly near the brake pads) and dislodge once in awhile when you reverse. When it happened to my car, the sound didn't completely go away until about a month passed. I'm sure the pebble just got smaller and smaller due to friction against the rotor and finally dropped out.