89 M998 "metal bang" noise seemingly from rear?

[NCarolinadawg]

(1989 6.2 3speed) Hello, since online health visits are on the rise, wanted to know what the community thought about my issue. I have some videos attached.
I have checked and 2 different mechanics have checked all bolts and nothing seems to be loose
The rear brake unit has no loose bolts that are rubbing or scraping on anything that can be seen or rubbing on the calipers.
The noise IS speed related as it get faster with acceleration and slower with deceleration.
I have had one mechanic diagnose it as a bad Transfer Case chain, he said he drained fluid and stuck his finger in the drain hole and could feel the loose chain and that it might be hitting the case but saw no metal shavings. I am about to the point of dropping the transfer case to see if that's the problem but trying to keep from "fixing this and fixing that" and end up never fixing the problem, so getting all the input I can. Is the transfer case chain a possibility?

 

[REF]

Just a shot in the dark here but, check your drive line clearance between the metal shield on the fuel tank and your shaft. Mine had a balance weight welded to the shaft and when the tank was full of fuel it would flex just enough to contact the weight and make metal clacking sound that was speed related.
I could not run your video or hear the noise But seems you have spent time looking for the common noise makers might be worth a minuet looking for a shinny spot on your drive shaft.
hope this helps

 

[NCarolinadawg]

Just a shot in the dark here but, check your drive line clearance between the metal shield on the fuel tank and your shaft. Mine had a balance weight welded to the shaft and when the tank was full of fuel it would flex just enough to contact the weight and make metal clacking sound that was speed related.
I could not run your video or hear the noise But seems you have spent time looking for the common noise makers might be worth a minuet looking for a shinny spot on your drive shaft.
hope this helps

I checked and dont see any scrapes or marks on the gas tank. No Visual signs of contact with the drive shaft against anything else.

 

[NCarolinadawg]

I checked and dont see any scrapes or marks on the gas tank. No Visual signs of contact with the drive shaft against anything else.

maybe this link will work. https://www.facebook.com/groups/777074789048826/permalink/3610051225751154

 

[papakb]

Two things come to mind. One is there should be a spring between the brake rod and the chassis to keep it from hitting things and grab both of the driveshafts and see if there's any play in them both vertically and horizontally. Bad U-joints can cause strange noises.

 

[Action]

Two things come to mind. One is there should be a spring between the brake rod and the chassis to keep it from hitting things and grab both of the driveshafts and see if there's any play in them both vertically and horizontally. Bad U-joints can cause strange noises.

especially check this...under the LH motor mount.