When going down the road while giving the ol beast (95) gas, everything sounds fine, until after I let it coast. then all of a sudden it starts making what sounds like a chatter or a whining noise in the rear end.

I changed the rear-end oil and did a 80/20 mixture of gl-5 and lucas heavy duty oil stabilizer and its still making the same noise.

I was wondering if when giving it gas and going down the road if that doesn't pull tension on the drive shaft, and when taking my foot off the gas and letting it coast if that doesn't cause that drive shaft to release that tension and cause that sound.

Thank you for your time and all help is appreciated.

Guess it would have helped if I said what year it was

 

First of all, check the u joints in the rear driveshaft. If that isn't it, then you probably have slack in your ring and pinion gear in the rear differential.

 

u joints seem fine. I'll take a look at the ring and pinion.

Thanks redneck!