Is it intermittent or constant? Is it only when you apply the brakes? If its not constant, I'm thinking it could be a warped rotor. Were your rotors cut the last time you changed the brakes?
Maybe someone here has other ideas that could help...
1988 GT - Stock
*SOLD* 2012 GT Premium, Black on Black, 3.55 Axle, HID and Security Package, Pypes Pype Bomb Axle Backs