The rear brakes on my 1995 Integra have recently begun to make a grinding noise on a regular basis. I even took off the wheels to see if the pads were completely worn down but they appear to still have a reasonable thickness to them. The rotors are scored but nothing outrageous.

Could this grinding be simply the result of a rusted/worn rotor (original rotors with 101k mi, mostly highway) or could this be a more serious problem?

Thanks
1995 Integra