need help identifying noise

[madkaw]

A little background; My 9/71 is just getting finished it's resto mod. I have only 200 miles since the resto and things are pretty good. The car drives wonderful and the engine runs super. Pretty much everything is new or rebuilt on this car-new tires,wheels,brakes, rebuilt motor.

My noise sounds like a tire out of balance or something that rotates is out of balance. The noise starts in about 50-55 and goes away towards 70. This is strictly a rotational noise, with no shimmy or shakes-nothing is felt while driving. The noise sounds like it is coming from the rear tire area, but it is hard to exactly pinpoint. I noticed that while driving in 4th gear at around 60, the noise is very prevelant, but if I shift to 5th gear and maintain the same speed, the noise about goes away to nothing(I have to struggle to hear anything at all). Go back to 4th gear and there it is.

I realize that all things should remain constant at speed from the tranny back, but would the gear change invoke a torque change that would change something in the driveshaft angles to cause an out of balance(long shot-I know).

It is fustrating to have this car run so good and drive so nice and to be paranoid about this noise.

The main driveshaft was balanced when shortened for the btw5 swap. The half shafts had the u joints changed 5k ago. I have an RT mount on my LSD.

Any ideas what to check? I had the tires balanced and rotated-no difference.

[Two80z4me]

check all of the bolts on the driveline, and also check your halfshafts for being loose at all.

[madkaw]

I believe the problem is my LSD. If I grab the halfshafts near the diff side bearings I can get some up and down play-worse on the left side. Never changed diff side bearings-is this difficult?