Had mine replaced too. Don't be surprised if you still have a slight whine with the new unit. Mine was decreased but can still hear it 45-55 under light accelleration and decel. Replaced at 2800mi. have 8200mi now with no increase in noise. I changed oil after 500 miles and again at 1500 since install. I think it is a good idea to change the oil as these gears do generate some very fine metallic particles during breakin.
2005 GTO, M6, Quicksilver / Black
2003 GTP, Silver / Black, 3.4" Pulley
1994 Z-28, Red, M6, Hotcam, SLPs, Tune
1994 Z-28, Red, M6, stock
1994 Cadillac STS