Brake pads scraping rear disc

I noticed when I rolled the bike into the garage today the rear brake pads were scraping on the disc. I replaced the pads about 1500km ago and this is the first time I have noticed it. Any idea's? Maybe I need to re bleed the line or the cylinder has pushed the pads out too far?

Does it bind up or just kinda rattle up against?

They are supposed to drag a little. most have the "floating caliper" and one side will rub the disk a little. No sweat unless it's dragging enough to cause binding or noticable drag.

Your rear rotor may have some warpage....

"Your rear rotor may have some warpage...."... Yup!
or a caliper that's sticking closed...

Raise the rear and spin the tire.... While observing the rotor from above, warping as in a warped album on a record player?

when you changed the pads...did you check to see how far the piston had ended up from the thin pads? did your old pads wear really thin? sometimes the piston get a little grime that keeps it from recessing with the new pads....did you lube the two pins that the active half of the caliper slide on?.....is you brake pedal adjusted to let off the push rod completely?......they drag a bit anyhow and make noise at first if it got wet,misty....ect....then sat and dried.......

One thing: they will drag if the caliper assembly is sticking on the pins it rides on. had to take them off my wife's car and clean the pins and regrease them because they were dragging a lot.