I've returned 3 Silver 15" rMBP for the same issue - cosmetic imperfections below the speaker holes. Its generally a scratch in the aluminum that was polished out but the finish doesn't match. Appears these are being rushed out the door and the fit and finish isn't up to Apple standards. I'm going to wait for them to iron out these manufacturing issues to buy again. If you own a 15 silver you should check for imperfections near the speaker hole array. Seems the machine they're using leaves a nasty scratch after its done!