Did the pads look glazed at all? Any discolored spots on the pads?
Probably picked up some road contaminant, got embedded in the pad material. Sometimes scuffing it up with some emery cloth helps, though that can also make it worse by embedding more crap onto the pads - better served by scuffing the rotor face, and having the rotor clean of the pads.
When my Hawk HPS pads start to squeak more than usually, I just take them out and bed-in the pads again - that usually cooks off whatever was stuck on the pad, cleans of the face of the rotor.
I think it's just brake dust b/c it comes and go. It usually squeak when the idle is high and when the car is not warm up yet and she starts to drive. When I drive it, it stop squeaking when it warms up. So I think it's just dust.
Thanks for the reply.