^ yes. Agreed - there appears to be a number of possible causes. Even after my dealer took out the pebble and showed it to me, the noise temporarily returned a few weeks after. I guess it's just a part of E9X life. I hope it doesn't come back again, especially at an inopportune time...
2008 E92 M3 6MT, AW/Blk Ext., brushed aluminum
2006 E46 M3 ZCP 6MT Carbon blk/blk(sold)
2001 E46 325Xi 5MT Jet Blk/Blk (sold)