Ok, I have a 08 mustang gt. well the front brakes were worn so i took the rotors to a machine shop to have them turned and i bought new brake pads. I wanted to go for the stock brakes but all they had in stock was Duralast semi-metallic. got the rotors back and put everything together. i have a habit of spinning the rotors when the jobs done to see if it grinds. it did. so i put the factory retaining rings back onto the rotors. the drivers side was good but the passenger side still grined just a little bit. figured id put another retaining ring on the opposite of the first to really tighten things down. haven't done that yet. driving around this week, everytime i apply the brakes they make a grinding noise. Im thinking its maybe because of that one rotor but im not sure. Anybody know?

 

Some pads make more noise than others. I'm not familiar with the Duralast pads so can't comment on them specifically.
If it were me I'd pop the wheels off and pull the pads to see if they are making full and flat contact with the rotor, to be on the safe side.

 

thats what i did but they were making good contact. my dad used to be ase certified and he said it was the retaining clips but ive heard most people throw them away cuz you dont really need them. so im thinking maybe cuz the pads are semi-metallic? my cousin thinks it could be a warped rotor but when i had them turned there was no problems