I have a 2003 Mustang GT and I have a few brake concerns. Under heavy braking I get a strange pulse coming through the brake pedal- the rotors have been turned and show no signs of warping. separately, I went to replace the seals and dust boots on the caliper. I put a block between the piston and caliper wall and stepped on the pedal, only one piston was forced out. Could one of the pistons be frozen?