My 1998 Dodge Intrepid has started making a

My 1998 Dodge Intrepid has started making a grinding noise in the rear end when braking. I had the brake pads checked at a garage and they said they were only 65% worn, no need to replace, they don't replace them until they're more like 90% worn. But the grinding is bad... it is worse when there are extra people or stuff (weight) in the car. It sounds like metal on metal to me. It kind of comes and goes, sometimes it isn't really there but most of the time it is, and sometimes it is really bad. A couple of times it has persisted even when I'm not applying the brakes.