I Need Brake Help!

[SupraSerious]

I have installed new calipers, pads, parking brake, and drilled and slotted rotors from brakemasters off of ebay. I'm starting to wonder if it was a bad decision because, now as i drive, a screech, not like a pad rubbing, but maybe metal on metal starts and stops, and increases in frequency the faster i go. I dont understand how, but after talking to multiple shops, no one has given me a clear answer. The screech may not been directly involved with the brakes, but it is coming from the back of the car, and i doubt the changing of parts and this annoying noise are just a coincidence...... So any ideas on how to stop it would be greatly appreciated!
Thanks!