[Bill04]

check for brake pads not being held down by the chromed plates on the rear of the calipers, you can do this by tapping gently on the inner edge of the front pads from the inside, the plates are supposed to put pressure on the rear of the pads to hold them in place, if not they click/pop once during slow speed brake apply, you should be able to see the plate move as you bump the pads if not theres to much clearence, recently replaced the right hand plate for exactly same condition, problem corrected.
Bill