Couldn't upload the video here. But here a YouTube link
https://youtu.be/IK28w9CjpEs
Just had the diff service and adjusted filled with redline 75w-90
CV axles checked and service new hubs new bearings new sub and diff poly bushings new comp clutch and flywheel. I have a solid driveshaft on the way.
EDIT: also have new trans mount and engine mounts installed new carrier bearing and still have the stock driveshaft in while waiting for the new one to come back.
Diff is a open case with a j30 vlsd in it.
What causes it, reverse and 1st mainly no noise in neutral or when you push the clutch in. Coasting At 4th gear doing 40 it vibrates from the rear end and same at 3rd and 30.
Thanks for any help