In Reply to: Diff whine posted by Ed Teller on August 26, 1999 at 07:10:07:
You didn't mention the maintenance history of you rear end. How many miles since the last change? ever? The correct weight is more important than the different kind of oil(synthetic vs. non). I think the correct weight is 75w90 for differentials.
Now, it is possible that with old(thicker)oil, you didn't notice damaged or worn gears, bearings,etc.,...New(thinner)oil will flow easier and might make the worn parts more noticeable.
I would make sure the correct wheight is in there and then see if you still have the wine. If so, a pro might want to take a look at your rear end(differential on your car!). Replacement of worn parts may be necessary. Make sure they know how to properly "set-up" a rear end.