A guy at a parts couter once told me a trick they used when he used to work at a brake shop.
They filed a 45 degree bevel on the leading and trailing edges of the pads. The bevel should be about 1/16 to 1/8 of an inch deep. It stopped my sqealing brakes and I have been doing it ever since whenever I put in new pads. Wear a dust mask, especially with the PBR's (which, incidentally, are good pads in my opinion) because they probably contain asbestos.
I think the bevel helps to stop the pad from "chattering" against the rotor when braking. Anti-squeal goop should be used too but it will not be effective if the brake pads are chattering badly.