What causes the Car to make a grinding sound randomly when braking? on 2004 Buick Rendezvous

I have had my front and back brakes pads replaced, rotors turned, caliper's checked, tires rotated, hoses replaced. The grinding can felt through the brake pedal and usually happens when turning. It happens randomly. I have not been able to link it to any particular driving pattern.

Asked by for the 2004 Buick Rendezvous
2 answers 1 comment
return for warranty something is wrong
My mechanic is going to check it out further. I thought maybe someone else may have had the same problem and could give us something particular to look for.
Poss. caliper missing bolt(s) and moving/grinding against rim when turning OR more likely bent backing plate touching rotor when turning.