Roaring/howling

Yes, it sounds like you have a pinion or ring gear bearing out which create a mesh problem for the gears which will only make noise under load. It is better at this point to just install a used rear end. But if you want to rebuild it here are some diagrams to help you see what is going on.

This video will show you how to get the axles out.

https://youtu.be/ytqXLSjHNm0

Install the new ring gear bolts. Tighten the ring gear bolts alternately and in stages, gradually pulling the ring gear onto the differential case.
For the 7.6 inch axle, tighten the ring gear bolts in sequence to 100 Nm (74 ft. lbs.).
For the 8.6 inch axle, tighten the ring gear bolts in sequence to 120 Nm (89 ft. lbs.).

Pinion Depth Adjustment

Tools Required
J 8001 Dial Indicator Set
J 21777-40 Rear Pilot Washer
J 21777-42 Front Pilot Washer
J 21777-43Stud Assembly Bolt
J 21777-45 Side Bearing Discs
J 21777-1 Arbor
J 21777-29 Gage Plate
J 21777-35 Rear Pilot Washer
J 23597-1 Arbor
J 23597-11 Gage Plate
Important: Make sure all of the tools, the differential side bearing bores, and the pinion bearing cups are clean before proceeding.

Lubricate the pinion bearings with axle lubricant.
Install the pinion bearings into the axle housing.

Assemble the following components into the axle housing:
For the 7.6 inch axle, assemble the J 21777-40 (1), the J 21777-43 (2), the J 21777-42 (3), and the J 21777-45 (4) as shown.
For the 8.6 inch axle, assemble the J 21777-35 (1), the J 21777-43 (2), the J 21777-42 (3), and the J 21777-29 (4) as shown.
While holding the J 21777-43 stationary, install an inch-pound torque wrench on the nut of the J 2177743 and tighten the nut until a rotating torque of 2.2 Nm (20 inch lbs.) is obtained. Rotate the assembly several times in both directions in order to seat the pinion bearings.
Check the rotating torque of the assembly. If the torque is less than 1.7 Nm (15 inch lbs.) , tighten the nut on the J 21777-43 until a rotating torque of 1.7 - 2.8 Nm (15 - 25 inch lbs.) is obtained.

Assemble the following components into the differential carrier bore of the axle housing:
For the 7.6 inch axle, assemble the J 21777-45 (1, 2) to the J 23597-1 (3) as shown.
For the 8.6 inch axle, assemble the J 21777-45 (1, 2) to the J 21777-1 (3) as shown.
Install the bearing caps.
Notice: Refer to Fastener Notice in Service Precautions.

Install the bearing cap bolts.
Tighten the bearing cap bolts to 75 Nm (55 ft. lbs.).
Rotate the J. 23597-1 (7.6 inch axle) or the J 21777-1 (8.6 inch axle) within the J 21777-45. The J 23597-1 or the J 21777-1 must rotate back and forth freely within the discs. If the J 23597-1 or the J 21777-1 does not rotate freely, disassemble the components, inspect for proper seating and/or mix-aligned components and re-assemble.

Check out the diagrams (Below)

Please let us know what you find. We are interested to see what it is.

Cheers, Ken

Yep loaded means while driving with a load on it. A free wheel test will not tell you what you need to know. I have seen mechanics use a gopro to help record the event.

Please let us know what you find. We are interested to see what it is.

Cheers, Ken