I got the same noise after the lift. I think it's just the driveshaft + thin floor. I also notice it more with the skid plates on - they probably reflect the sound back.

Check your fluid levels - replace axle oil if its been a while - as well as the TOD case.

Check the U-joints (see if there's any play in the drive shaft when you try to turn it by hand...)

Check your emergency brake tension

Check the rear rotors - discs for corrosion


Check the inside of the rear rotors for a loose drum pad (E-brake) or worn pad.

If all else, maybe rear bearings....

Also, meet up with a fellow VXer and try their ride to see if it's they have same noise....

Good Luck.