on my 660R the plate on the end of the chain adjuster (RHS) had come loose and been rubbing and grinding itself against the sprocket bolts!
I guess if I had been washing the bike more frequently, the damage might have been avoidable. For now a new plate is required!
This happened once before when the bike was less than 6 months old.
My question is what did I do wrong at my last chain adjustment. Both the rear axle and the locknut were torqued as per spec