[G.A.S.]

Ideas:
bad wheel bearing, jack up car and grab wheel and try and move it up and down/side to side.
Brake pad came off its backing plate/brakes are worn down to the pads backing plate.
Pull off tires and inspect brakes.
did you ever notice anything strange with the brake peddel?
start like I discribed and post back.
You will most likley find bad pads.