its the inside pad on the caliper piston...
clean the back of the pad and the piston , then put a dab of silicone
on the pad where it makes contact on the piston. put it back together.
lock the brakes if you have a park brake for about a hafe hour.
then release. and adjust the adjustment screw in on the back of the caliper
til the brakes start to drag , then back off a 1/4 turn. do each wheel.
then your done. no more clacking.......