I own a 1993 jeep country. It makes a loud rattling noise coming from the transfer case even when it's in regular drive. It sounds like the bottom is going to fall out. A new chain was put in it when I bought it used a couple months ago, but the 4 wheel drive has never worked right. I haven't even used it. What could be wrong and will it hurt if I drive it? It runs quieter in 4 wheel drive. At first it ran fine in regular drive. Also can I get a diagram of inside the transfer case?

check the front drive shaft spline or "U" joint at the transfer case
splines on this shaft wear more quickly that the rear drive line
as the operation angles for the front diff are more acute that the rear shaft

make sure that the inside of the rim is tight on the hub and not sitting off it
loose/ incorrect wheel stud nuts will also cause the noise

Could be catalytic con.in side.

sounds like the transfer case is broken.

Harmonic balancer.

I had a 4x4 year ago. Do you have front locking hubs ? I don't think so if you did I would ask if they were in or out. If there is nothing else It has to be coming from the transfer case. As far as I know no manufacture makes a true 4 wheel drive but Jeep except for maybe Raptor or Power Wagon. Most come with an open diff in the rear one wheel drive unless you order it special and the front you can't even order a locker if you wanted to 99.+% of 4x4s have open diffs in the front. Jack up one front wheel and one rear wheel if you didn't order a special rear end if you try to drive off the jacks you will sit there and spin your 2 wheel drive and not move.Ford says if you have worn tires or not the same air pressure in all tires it will do this. I think you have a bad u joint or pieces broken in the transfer case or it is out of adjustment. Jack car up like I said before and when the wheels spin without pulling it off the jack stands crawl under and see where the noise is coming from front or transfer case.I wonder if your shift motor could be bad they are about 65 dollars

Sounds like you broke a gear in the transfer case you will need a tranny shop to check it.

Sounds like the fluid coupler inside the transfer case failed. In my opinion using those is a great idea
on paper but they just do not last as well as the older direct engagement units used in Cherokees and wranglers. I own many Jeeps and will not have a GC for that one reason.
The transfer case needs to be removed and rebuilt. There is no external repair or temporary fix.

Give a try by change your transmission/filters and Transfer case oil.

sounds like you have your transfer case on a bind i would take it back out and see what is holding it up from shifting