I noticed a scraping sound coming from the rear of my bike the other day while riding down the road at about 35 mph.it sounds like a rotor being turned on a brake lathe,i press the rear brake pedal hard it stops making noise,i let off it starts again.sometimes not as loud.the caliper has slight movement on the bracket.i sprayed the rear wheel and caliper with high pressure water,it helped quieten it down,but still makes noise.i'm going to remove caliper and clean with brake cleaner to see if that fixes it,does anyone else have any suggestions?

 

Sure it's not the sound of the disk rubbing against the pads? Sounds like a piston is not returning to it's "home" position all the way if it's making that much noise running down the road. Is the disk getting hot? Uneven wear on the pads?

 

it doesn't get hot ,you can touch the disc.if I twist the caliper around by hand it doesn't do it until I use the rear brake a couple of times.i was thinking the piston is not releasing fully as well,just trying to get some opinions on how to fix this without putting it in the shop.i recently bought the bike with 275 miles from local dealer,it has warranty until Jan.the weather is too nice to have it down for repair right now.

 

It's more than likely the brake pads just passing over the cooling holes in the brake disc. IMO it's nothing to worry about. You should also notice the front brake sounding somewhat the same.