The rear brakes started making a howling sound when applied. After five miles, while I was backing out of my driveway, there was a loud 'clunk' and the brake pedal went soft. I then discovered a brake pad had fallen out of the right rear caliper and was laying in the street. The repair shop told me that the metal retainer clip had broken causing the pad to fall out. The rotor and caliper were damaged and the entire assembly had to be replaced on both sides of the car. The Volvo dealer supplied the new parts which included upgraded, ventilated rotors. According to the parts department staff, the original rotors are prone to overheating causing the retainer clip to fail.

The fact that Volvo supplied upgraded rotors leads me to believe that they are aware of this problem, and I believe some formal action should be taken on their part. Had this happened at a higher speed, it could have caused an accident.