Diagnosing noises in a torque tube axle is a little tricky, since nothing is really accessible without some disassembly. On a conventional open driveline, you can inspect things like universal joints and the pinion flange of the rear end by simply putting the vehicle on a lift and moving and shaking things. About the only thing you can do to check for looseness in an enclosed drivetrain is to put the vehicle in gear with the engine stopped and try to roll it back and forth, looking for slack somewhere. Dropping the rear end cover plate lets you look at the gears and inspect the lube oil for metallic particles, etc., and you can use a magnetic base dial indicator to check for excess slack between the ring and pinion gears.
Now, for noise interpretations- - - -this gets to be a tricky subject, as there's a lot of overlap between parts that can cause similar noises. A steady whine or rumble that doesn't seem to change with throttle load or when coasting in neutral can be rear wheel bearings, or the carrier bearings on each side of the differential case where the ring gear mounts. Noises that increase or decrease with throttle opening are usually related to loose or worn pinion bearings. Worn gears can also create noises that change pitch or seem to go away entirely when the throttle is moved from "pull" to "float" to "coast". I've been listening to rear axle noises since the late 1950's, and I still get fooled on occasion. A torque tube rear end has only one universal joint, and it's contained in a ball-shaped housing at the rear of the transmission case. It also has a roller bearing or a bushing and a seal in the torque tube right behind the u joint. Wear or damage there can also mimic rear axle troubles. I'd begin a diagnosis by inspecting the gears, bearings, and lubricant by dropping the rear cover plate. One sneaky trick to get a good look at the condition of the lube is to put a little of it into a clean white Styrofoam coffee cup, and shine a bright flashlight at the bottom of the cup. Metallic wear debris makes the lube in the cup look shiny. That's not a good sign! Good luck!
Jerry
