Heres the deal. In my time I have broken 6 sets of gears. I've heard just about every whine, clunk, thud, crash and bang a rear can make but I'm having trouble pinning this one down. The noise sounds just like gear whine. High pitch and no growls. Starts at 50mph through 80mph and only under acceleration. The kicker here is I got the EXACT same noise with two completely different rear ends. One was 7.5" and now with the 9". The rear u-joint on the DS has been replaced and that did nothing. THe sound is very clearly coming from the back of the car. There is no other vibrations or odd noises associated with it.

So, anyone ever come across something like this? Maybe the trans projecting noise down the DS to the rear? tires? DS? The 7.5" rear I took out and put in someone elses car and it make no noise at all so IMHO that pretty much eliminates the rear end from the noise... I could be wrong though.

 

Same here! Replaced rear end with an lsd 3.42, and had my tranny rebuilt at the same time. sometimes I get a horibble grinding noise in reverse. Symptoms are exactly the same.

 

Sometimes, I listen to Car Talk on NPR. There have been instances of the "mystery ailment" in somebody's car that just suddenly started happening. Upon getting the folks to think back or investigate, they find the real cause of the problem.

For instance, there was a lady who was having trouble starting her car. So she had it towed to the shop and the mechanics had no problem. Her husband had no problem. So hubby called in to the show to let them know what really happened. Turns out that immediately prior to her having the starting problems, she had put new floor mats in the car. What does that have to do with it? It prevented her from pushing the clutch all the way to the floor. The big, strong men had no problem pushing all the way. The fix? Hubby pulled the floor mat down a little bit. Voila! No more trouble.

So, that finally brings me around to asking: Is there anything else that you did immediately prior to the noise that might not seem to be the problem but just might in some crazy way?