Lifted, and big tires, neither of which was my problem.

My rear axle was out of alignment, from going offroad, alot. There are (for all intents and purposes) 3 rods that hold your rear axle in place. 2 go front to back and 1 goes side to side, well I bent them ALL ! This was causing rear driveshaft vibration.

We took them off, straightened them with a jack, and have been good ever since. I noticed a similar noise recently, faint but growing, but I greased all the fittings on the rear driveshaft and it went away.

Brian