I just replaced both my rear rotors and brake pads on my 03 Impreza RS. I replaced them because I was having a loud high pitched noise coming from the right rear wheel which I believe was caused by the rotor and brake pads being in bad shape, and this seems to have solved the whining problem. The weird thing was that I replaced my brakes about 2 years ago and they only had around 15,000 miles on them, the left side pads weren't too bad, they had maybe 50% life still, but the outside right rear pad was really worn down.
When I finished installing everything I went for a drive and immediately I noticed a scraping or rubbing sound coming from the rear end (it just sounds like the brake pads are scraping when I not touch the pedal). The sound goes away when you speed up and after driving for 20 minutes or so the sound no longer happens when driving straight and slow only when going slow and turning. The noise goes away completely when I press the brake pedal. So my question is, could this just be that the brakes need to wear in or maybe grind down a little bit to stop rubbing? A mechanic told me that if my caliper was bad and causing excessive dragging then my rim should be hot after 10 minutes or so of driving but the wheel wasn't hot. This noise was not happening before I did the brakes so I'm assuming it has to be the brakes dragging. Any help is greatly appreciated.