Sorry, didn't realize you already had your pads replaced. I understood it to mean that you didn't but they needed to be replaced. It could very well be the retaining clips. It's worth checking out anyways. I had a clip that wouldn't hold the pad on very well once and I did something I probably shouldn't have done to fix it. The pad was somewhat loose and vibrating against the caliper whenever I was driving. It wasn't really that loud just annoying so I took the pad off and sprayed the backside of the pad with some rubberized undercoating from a can. I then reattached the pad and the sound went away. I don't recommend this but since you had your pads replaced at a shop then I would ask them to replace your retaining clips.