i installed slotted/c-drilled rotors and ever since i hear a constant "thudding" sound, kind of like when you put your finger in a fan blade and it slows to a stop. when installing i made the mistake of not screwing down the rear caliper pistons. instead i opened the valve and c-clamped the rear one's down while letting the brake fluid squirt out, and replaced lost fluid in the reservoir. maybe i siezed the piston? any idea's or comments