I have a 2005 Trailblazer which I changed the rear rotors and brake pads about a year ago. I cleaned and greased the pins and they moved freely. I cleaned the pistons and the boots all looked fine and the pistons moved freely as well. But I did have some corrosion on the end of the piston on 1 caliper which actually caused raised bumps on the end face of the piston which presses on the brake pad. I filed and sanded the piston end flat and smooth so that the whole piston would contact the brake pad evenly. Now for the current problem, I have about 7,000 miles on the truck since the brake pad and rotor replacement and both rear brake squealers are squealing when the brakes get hot. I took off the rear wheels and inspected the brakes. The pads are fine (almost look new) but the rotors have worn down tremendously to the point where there is a deep groove that the pads fit in but the squealers which sit just beyond the pads are hitting the rotors causing the squealing. Anyone know why the rotors are so badly grooved yet the pads are fine with so few miles? Do I have a problem with the calipers and should I just replace them. Obviously, I know I need to buy new rotors but I do not want to have the same problem occur to the new rotors. I need to fix whatever caused the rotors to get an 1/8" plus deep groove with just 7k of driving. Thanks for the Help!!