I had a similar screeching/grinding sound coming from my front brakes. My car only has 1,200 miles on it but I was driving and heard this insanely loud sound coming from the brake area. Pulled over and saw everything was clean as a whistle, continued driving and wiggled the car around and the noise went away. It must've been a rock or something trapped in the rotor or caliper.
__________________
|2013 Audi S4|Ibis White/Black|S-Tronic P+|
|2013 370z|PearlWhite/Persimmon|Touring/Sport/Nav|F.I. CBE 18" CF|
|Sold|2011 370z|Gun Metallic|Touring/Sport/Nav|
|