Welcome to the Stovebolt Grampes cool

I am suspecting the center support bearing may have a worn rubber in it,,,,,(That sounds bad)
I mean to say is the rubber surrounding the center support bearing on the driveline is worn or loose.
Be sure to have the wheels blocked before crawling under the truck.

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You may also block the front wheels, rais the rear wheels off the ground and spin the driveline and wheels by hand. Listen for noises and where they come from.

There is enough good in the worst of us and enough bad in the best of us that it does not behoove any of us to criticize the rest of us.
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Be yourself. If you are ever lost, It will be much easier to find yourself if you know who you are!