Several have had the same problem, including me. I replaced the u-joints, had the drive shaft balanced, replaced the u-joints again thinking I got a bad one and finally had someone who knows tell me about the angles. Per the off-road shop and the drive shaft and axle shop the angle is not too great but the angle out of the transfer case and the angle of the rear pinion are not the same. Adjustable links or a custom built shaft with cv's instead of u-joints is the only answer. greasing your nips will keep it quiet for a short time, mine only lasts for about 100miles.

Disclaimer: I am only repeating what I have heard when asking about how to fix mine. I have not done anything with mine yet.