As I got home yesterday and rolled onto my drive, I heard what sounded like metal dragging along the tarmac. Bummer, I thought, the exhaust has dropped off. Got out, had a look, no it's fine. Have a look under the car, around the wheels. Nothing. So what the hell is making that sound? Get back in, first roll off the drive with the engine off and windows down. Hmm, coming from my side. Switch the engine on and drive a few hundred yards. Sounds like it's something banging against the plate behind the brake discs. Back home, raise the offsite rear wheel and spin it round a bit. A sodding pebble has got in between the farside of the disc and the protective plate / fairing, and will not come out! I guess in time it will wear down a little and pop out. I assume it can't do any damage back there?