I just got a set of BB5s for my MTB, were great for the first 75 mi, but now the rear sounds weird on hard braking...it sounds like its down to the backer of the pad, but its got almost all of the friction material still on it.... No odd marks on the disc either.... Any ideas what may be causing the odd griding sound on the rears only? Fronts are fine..... Shot of the bike:
