Rear brake humming

Right rear brake has a humming noise when coming to a slow stop, replaced all brake pads all four wheels 8/8/2013 just changes rear rotors 8/14/13, thinking this would make noise go away but once brakes are warm the humming noise comes back. It also appears that the pad does not contact the entire rotor looking and the stopping marks on the new rotors as well as old rotors that were removed.

It is only the right rear wheel that makes noise though.