did you take all the pad rails off when you stripped them down??
as this is what causes the pad to get trapped, they oxidise so bad behind them rails and gradually push the pad rail out and cause the pad to squeal as well.
mine hardly ever squeal due to keeping these rubbed down and copper grease on the pads, but some frp's squeal non stop i dont know how they put up with it
pumabuild used to stock the shims but think they have all gone, must be someone who can supply them? alcon maybe.