in some cases its the pads rubbing on the pistons and mounting pins. most cases its the pad and rotor contact making the noise.it all depends on how much metal is in the pads and how perfect the rotors are. i have mine turned when new before i install them.(you would be surprised how often you get a new rotor that is imprerfect) DO NOT HAVE CHECKER,AUTOZONE OR ANY PLACE OTHER THAN A MACHINE SHOP TURN THEM. most of these places are careless. there is a spray made by i think crc that you can also spray on rotors that is supposed to help with squeak, but i have never used it so i dont know if it works or not.

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