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Dear James, I have a 2005 Pontiac GTO with a 6.0 liter engine that makes no noise going down the highway. It only makes noise when I turn a corner or do slow speeds turns in a parking lot. I have had all the fluids changed in hoping this would fix the problem. I still have the noise and have no idea what to do next. RC, Panama City,

RC, without hearing your noise I can only give you a guess to what the noise is. I know that most GTO’s come from the factory with a “Limited slip” rear end or differential. This means that both tires have traction to the road when you give it gas. To verify that you do have this type of limited slip rear end, you need to find a dirt road so that you can see if both tires “grab” when you take off fast. If they do, then the problem may be as simple as adding an additive to the rear differential to allow the wheels to “slip” when you take a corner. Let me explain how this type system works: When you go down the road straight, there is no reason for wheels to “slip”. But when you turn a corner, one wheel is going to travel more than the other. To allow the one wheel to travel more than the other, there needs to be some “slippage”. In order for this to happen quietly, the rear end has clutch discs that allow it to slip ever so slightly without making noise. In my experience if there is not enough “limited slip additive” added to the differential, then the wheels will make a grinding, rubbing, and scraping noise on turns or while performing parking lot maneuvers. The differential grease without this special additive is not slippery enough to allow this controlled “slippage” to happen. This is why it is mandatory to add this special synthetic limited slip additive to the differential to keep from tearing up the clutches in the differential. This additive will allow the smooth slipping of the clutches without noise when you are turning. I suspect the shop did not realize that you had a limited slip differential in your car. It is recommended to change your differential fluid every 30,000 miles or 2 years due to the limited slip additive will slowly deplete to the point your differential will start to make noise. Hopefully adding this additive will solve your problem and all will be well. If the noise gets better and yet some noise is still present, then the clutches in the differential may have been damaged to the point they must be replaced. Peace and prosperity, James Morris


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