Installed a Rough Country 4" lift. Lowered the transfer case and everything was fine. Changed gears from 3.08s to 4.10s and I now have a growl (notice a slight vibration)from somewhere under the truck. I don't feel or hear it under acceleration. I notice it when I let off the gas and coast (most noticable at about 60-75 MPH; sometimes aroud 45). Changed rear U-joint, had ring and pinion checked (twice) and its still doing it. Could it be an axle bearing or could it be a drive shaft vibration? Again, I only notice it when I let off the gas. Any ideas?