I have been chasing down noises for over a month now and I'm completely spent.
I have a '97 Ram 1500 4x4 Club Cab Sport 5.2L 46RE auto. It started making some odd, really loud rattling and clunking noises under the cab. Initially, it sounded (to me) like it was trying to engage the 4x4 on it's own, but having trouble.
It does kick a little hard when shifting into reverse, but my 95 did that too. When driving, it usually shifts really smooth, although, occasionally, it will hang in a gear too long before shifting to the next.​​​​ Then the noise starts, as if someone dropped a large wrench into a moving gearbox. It rattles, it clunks, it occasionally sounds like a couple years are spooled up, but having trouble engaging, thus chattering a bit. All the while having NO noticeable effect on how it drives. While the noise is happening, I can romp on it and the noise stops for a bit. Once I get up to speed and level off, it usually quiets, but it may sporadically make a rattle or clunk, but not constantly. I'm uncertain if it's related, but when coasting, like slowing to stop, there is some vibration for a bit that ALMOST sounds like a heat shield rattling, but the vibration effects the whole truck. This, I figured, may just be u-joints, which I have, but haven't installed them yet and it has a brand new Magnaflow cat, so that's not it either.
Pulled out the front shaft and disconnected/plugged the vacuum lines to the actuator yesterday and took it for a drive, hoping the noise would stop, but it didn't.
I am at my wit's end here. I just got this truck back in October. The following week, the cat plugged up a hundred miles from home and it sat for a month and a half at my mom's house due to the tow truck driver planting his hook directly into the axle joint and breaking it. Once that was fixed, I finally got it home and this problem started. Seems cursed lol. Apologies for the long read, but if this mystery gets solved and fixed, it would be greatly appreciated!

 

Check the u-joints in the rear shaft. If you have a two-piece shaft, check the center support bearing as well, the rubber degrades, and even though the bearing may still be good.... the bearing isn't supported properly, and things get weird.

Another thing that you should look at, if the u-joints are ok, need to drop the rear driveshaft, and pull the tailhousing off the transfer case. There is a snap ring on the output shaft that likes to disappear, and allow the shaft to walk. This allows everything on the shaft to move as well, and it can grind against various things, (including the back of the case.....) and tear them up. Eventually, the t-case will simply blow itself to bits, and if that happens on the freeway, life gets REAL exciting, REAL fast. (and you will need to change your pants......) Check it SOON.

Welcome to DF!

 

Thanks for the welcome and the suggestion!
The shaft is a single piece and has no play at all. I have new u-joints for it, just as a preventative measure and will be putting them in soon...if i can figure out the noise and fix it. It's been parked for the most part, not wanting to risk a breakdown, ESPECIALLY after my neighbor rode with me last week to see if he knew what it could be, since he's fairly familiar with Rams. The result was "I'm not sure exactly, but whatever it is, is gonna make itself known big time."
The test run yesterday was just a 2 mile run to take the trash to the dump and see if removing the front shaft helped.
I will DEFINITELY pull that off and look. It kinda would make sense since (I failed to mention it before) if you grab hold of the 4 wheel shifter, you can feel whatever it is with every single clunk and rattle. That's what led me to think maybe it was trying to engage the front axle.

 

If you can feel it in the shifter, go for that first off. Transfer cases don't go bad often but when they do, they are quite rude about it.