This might not be the case, but you can check and see if the rotor cover is touching the rotor. Sometimes they can get warped over time.

Also check your calipers. Sometimes they can get rusted shut, and end up freezing, also making noise. This wears out the brakes quicker too.
I think you would have to remove the pin that holds the caliper, and sand it down and WD40 it to fix that if its the case.