There is not a carrier bearing on his rodeo.
4" of lift is not excessive,have you checked your rearend fluid?

While under load could it be an exhaust heat sheild vibrating?The Turtles sheilds came loose and caused a weird vibrating whiney type of noise......a couple hose clamps around the front two sheilds cured that.It did it real bad while excellerating from a stop.....bad harmonics I guess.

That was a leap towards the cheap side of possiblilities. <img src="/forums/images/graemlins/smile.gif" alt="" />

Hope that helps before you dive into the rearend and start checking bearings for flat spot's.
Goodluck

Bansil