Sounds like cheap pads to me, try a set of Jurids or Textars.
I'd also make sure you didn't hamfist the backing plates. I've seen these rub lightly while rolling and due to deflection in the bearings while braking make contact with the rotor, the result.... it sounds like a garbage truck stopping.
I've also seen these make noises only under turning loads.
I'm a firm believer in OEM vendor parts which is not that hard to figure out.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.