it could be a number of things like warped rotors,brake caliber,or the brake line. on my g-ride when i applied the brakes they did not release which gave me the metal to metal sound. It came to be on the driver side the brake line went bad it was letting pressure on but not of. On the passenger side it was the the caliber sticking, which both together made me go through a set of brake pads in about a month. Hope this helps you out.
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