Gear change and rear end noise.

[bhedberg]

After having 4.10 gears swapped into a 1990, I am experiencing a very loud low frequency hum at highway speeds, the faster the louder. I got the gears from Al Kindler years ago. The build replaced all the seals and bearings and was performed by ctaxleservice.com in Ellington CT. The loud hum is so persistent as to make a long highway trip something not to look forward to. The noise does not appear to be related to anything except how fast the wheels are turning. It is the same regardless of the gear you are in, whether accelerating or decelerating, or just coasting. I suspect there is some issue with the setting up of the gears but I am not sure. Is it possible a wheel bearing could do that? Also, I am not sure I got the half shafts in the same orientation with respect to the yokes or not. Could something like that be related? Does anyone know who I should be looking for to have the problem properly evaluated and diagnosed? I hear people talk about gear whine or clunks etc from differentials, but have found nothing similar to what this car is doing. It is a lot of work pulling the diff, I'd hate to do it again and still not get it resolved. I am reluctant to take it back to the fellow that did the work because I am most interested in getting it fixed rather than having a battle. Any suggestions appreciated.