I had picked up a cheap waterproof GoPro case (because the SD card dust flap had long since disappeared from my old Session 5) and magnetic gimbal-thing to video some desert dunes stuff. I had put it under the rig when crossing the Mojave river to see if it was even deep enough to get submerged. The riverbed was so filled-in by a Union Pacific railway maintenance team that it does not. When I played the video on my phone I heard a metallic pinging sound that has me interested. Not sure what it is yet, but I may ask for advice so I put the video on YT. I'm just testing whether the Embed link works on this forum. I work in IT but I don't really spend anytime using this technology stuff so bear with me. Maybe it's just the camera or the mount - I will be testing different things, but the sound is not present when attached elsewhere on the body. A recently installed TC skid plate sits about 1/4" from from the case (with the stock 'skid' removed) so I'm wondering if it's banging on that. That or a driveshaft? I would have been in 4-High. It is an unpleasant video to listen to as the wife just let me know several times....

Not like anything I've heard before. It very well could be your skid plate, but I feel like you would've noticed it in the cab at that point. Is that mounted near the gas tank, like under the left rear seat? There are a couple hard lines running up there along the frame - fuel and whatnot. Might be them rattling around, maybe?

Hmmm - that could be. The thing was mounted under the driver's side near the fuel filter/lines. I might have to drop the TC skid and see if there are marks but I'll probably put the gopro down there again the try to get a better idea. I don't hear anything in the cab. I believe I had it on the frame rail so it may be transferred sound......weird.

The sound almost seems to correlate to the wheel moving... Maybe... Might be a good idea to check the torque on everything down there as a good start

It sounds like the transfer case harmonic balancer rattle.

I second the possibility it could be the tcase harmonic balancer. I could hear mine with window rolled down clanking around. Good luck MikeM

This seems credible. OTOH, the noise (to me) is also consistent with a rotating part contacting a stationary part. Prop shaft vs. gas tank skid?