Originally Posted by mkoesel
Has anyone ever actually been able to either see the pebble stuck in the brake shield by using a small trouble light, or removed the shield to see the pebble fall out?
Obviously some of these cases are pebbles, and some are not. For some folks who have recurring problems, it seems more likely that it is something else that happens to come and go. I realize other causes are discussed in this thread already, but it seems the vast majority of folks are willing to buy that it is a pebble in their case without ever really being able to verify it. Just an arbitrary, salient point to consider.
I have personally removed a pebble 3 or four times. I have also seen a similar instance where it was actually the heat shield making the noise at the track on someone else's M3. I pushed the heat shield back a bit for them and the sound went away.