I had some odd squeaking back in the day from a set of pads I had on. I picked up a can of disc brake quiet, which is this blue stuff in a can. Took the pads off sprayed the backs with it and it stopped.
Do you put anything on your wheels, like the armorall wheel protectant? I used to do this and for a few hunded miles after my breaks would squeek just before stopping. Then I plasti-diped them so not I never have to go through the embarasment.