Pulsing noise coming form the rear of truck

I’ve started to notice a pulsing noise coming the rear end of my truck when accelerating around 60+ lately and I’m having some trouble tracking down the problem. I originally thought it was my diff since I just had east coast gear supply rebuild it and after the 500 mile break in period and about 1000 miles after that I had vibration from 60+ that got worse with speed and a slow pulsing noise (about a second intervals). Even after sending the dif back, since it was under warranty, the pulsing noise was still their bud no vibration so I did the rear wheel bearings which were going but that wasn’t the problem. The only other things I can think of are a u joint is going bad or maybe the difs fluid level is to high. Since the truck is lifted 6in and the fill plug on the axle is much lower I parked the truck on a incline and filled it but I’ve tested the truck with normal fluid level and about normal fluid level and the noise is still there. Any thoughts on what could be the problem?

 

Belt in a tire, maybe

 

The noise also comes in around 40-45 sometimes but goes away it the speed range. I seem to remember testing the truck out on a different set of tires and my current ones have been balanced in the last 6 months but it could be

 

Maybe just switch tires front to back and test again? Tires seem to be the next culprit worth ruling out

 

Have you inspected the center support bearing? Referred to as the 'carrier bearing' on TW.