I started to hear a noise coming from the rear wheel area over the weekend. Not loud, like a pulsing/humming noise (not the normal metallic brake sound) that gets faster or slower depending on the speed. Can only hear it when going slow. So I felt the rear brake rotor and it's pretty damn hot, like exhaust hot, even when only out for a short trip. The bike has 1900 miles on it and it didn't do it when it was cold out but now that it was pretty warm over the weekend I started to notice it. It doesn't feel like the brake is dragging and the bike doesn't slow down because of this.

I know the pads sit very close to the rotor but it shouldn't be getting this hot. Brake fluid being hot and expanding? Any suggestions?

Thanks