Differential Noise?

[BHutch]

The noise is a rumbling or growling that happens on very light throttle, when the driveline is just barely loaded. Any more or less throttle, the noise goes away. Is most prominent at highway speeds. It is not apparent at speeds less than 40 MPH. It's very difficult to pinpoint where it is coming from but seems like the rear. Sounds a little like knobby tires running over rough pavement. There is no vibration associated with the noise.

My initial thought was axles based on threads in this forum. Unfortunately, a pair of CVJ axles did not cure the noise, although my old axles leaked so replacement was not a waste. During axle replacement a new differential mount and Mobil 1 gear oil were added. Flex disks and center bearing are less than a year old.

I have a hard time imagining what else besides the differential could make the noise under those conditions. Wouldn't bearings or suspension parts be independant of throttle?