Remember the grinding noise topic recently? At low rates of speed, like in parking lots while turning? Well, according to the service manager...a bulletin had been issued re: changing the rear end fluid which they did & say it should take care of the problem, haven't picked it up yet BUT we'll see! Now keep in mind, this car only has 5000 miles on it & they gotta change out the rear end fluid hummmm?

 

I've been dealing with this for six months or so with an early '05 model C6. Seems that the rear end has a series of small clutches, and the original OEM oil foams up and doesn't provide lubrication as designed. My dealer tried a non-foaming oil which provided temoprary relief. Then, recently when problem reappeared, Chevy has acknowledged problem and developed a substitute oil which seems to be doing the trick. Have now gone 2500 miles since most recent fix and so far no problems.

 

Many limited slip differentials in the past had a distinct "gears turning" type of whirring noise, rather than a "gears" grinding noise, which I imagine is what you were hearing. I suspect that, back in the 70s and 80s, that noise was a marketing plus ("Hey, listen to that! I have one of those rare limited slip differentials!") but today silence is the goal.

I would take the dealer service rep at his word, a change in fluid will probably fix the problem. It is worth asking if the fluid foaming associated with the noise did anything to durability. Regardless, keep the receipts for the repair unless you ever have any other prlblems with the rear end -- you may have a claim even if the car is technically out of warranty.