700 miles is no way enough to fuck a diff with the wrong TYPE of oil in it, especially in a road car. Wrong WEIGHT of oil maybe...

Grippers are noisy fuckers as it is, especially on tight corners, as they use preload plates and not planet gears like ATB's. They lock up shit loads nicer than ATB's too so i say you've got a better deal out of it.

as said above, if it DOESNT make noise, then its not working properly.