New brakes/Loud screech when turning

Hey guys. I just had my rear rotors/pads replaced. I thought one of my calipers was bad but my mechanic said is was just rusty guide pins not allowing full travel. So anyways my problem is whenever I make hard sharp turns it sounds like the breaks are rubbing bad. Its a loud screeching noise. Any ideas what might cause this?

My car does this too, I noticed that its the rotor coming into contact with the caliper mounting bracket, and the calpier itself is "floating" just fine. There is a GM TSB from a while back thats says to shim the mounting bracket at where it bolts to the axle tube. My problem with this fix is why would that distance change, I'm thinking worn bearings, c-clips, or maybe just aftermarket rotors are thicker, maybe a combination of things. Anyone else having this problem?