I love the people who insist it's rocks between the heat shield and rotor. Everytime something goes wrong with an M diff which is more common than you'd think, forum guys blame rocks. Obviously this is not rocks just like it wasn't with E9x M3 diff issues.
Now if it's a clunk, that's another story. That's totally normal and has been that way since E46 M3.
__________________
///M Power
|