What I've seen typically is there are brake pucks or adhesive disc called "damping shims" that are attached to your original pads. When you removed the pads they will sometimes stay in the caliper cup and more often then not they come out with the pads as they have an adhesive backing. These "pucks" do not allow the pads to shift back and forth in the caliper. Just a thought as I have performed many brake services and most recent being a 993 in which I remember them coming off rather hard.
-Ty
*Speed Yellow 986*
