Car Noise Help

Jeep 2000 Cherokee

So I have this thumping noise, almost sounds like something is loose.
The noise occurs for a few seconds when I accelerate from a dead stop and then goes away, it returns when I slow down and almost come to a complete stop.
The noise also goes away when I put her into 4wd.
The thump/rattle sounds like it is coming from the center counsel area and directly under the floor board in the driver seat.
My car changes gears smoothly up and down while driving.

I was told it might be a transfer case problem and that it might need to be rebuilt, which makes me worry.

I presume your car is rear wheel drive in 2WD, so has a driveshaft. That’s like my 4x4 Ford truck. It has occasionally had his exact same symptom, and it’s always been a defective u-joint in the rear section of the drive shaft. But there’s u-joints in the front section two, which is pretty much right where you are saying you are hearing the noise.

What I’d do if this was my Ford truck, I’d block it up on level ground so it couldn’t move, crawl under there and twist the driveshaft one way and the other, see if there is any play. There should be no play at all when you do this. If there is, you can usually readily see which u-joint needs replacing.

Check your engine mounts.