Noticed some grinding type noise coming from the rear the other day. Took it in and found that all four inboard brake pads were shot and the rotors were all damaged from the metal on metal from the pads. Apparently, from what we could see was that the rotors had alot of rust on the inside. That wore the inboard pads down and when they were pretty well gone, then they damaged that side of the rotor. So four set of pads, four new rotors, brake fluid flush and wheel bearings packed later, I left there with a much lighter wallet than I went in with
I have less than 22k miles on it, have had the brakes checked by a Ford garage at least once a year and had the Brake fluid changed every other year. The calipers were working fine. It appears to be strictly caused by the rust that built up on the rotors. Now what caused that rust to build up is anyones guess. Although I hear it is not that uncommon even on cars that have high miles on them. I am guessing that when the Ford garage "checked" my brakes in the past, they only looked at the outside pad and thought everything was fine. I had asked them just a couple of months ago to check the calipers when they did the brake fluid flush. So I doubt they checked the calipers or they would have seen the inside pads being almost shot at that time.
So look closely at the inside of your rotors and check the condition of those pads.