4wd is very loud, has a hard time going back to 2wd.

Ok so I have this '99 4runner that I bought used and 4wd was seldom used, if ever, over the life of the vehicle. It engages in 4hi but when it does, it's pretty noisy. I've never owned a 4wd vehicle before so didn't know if this is standard. I figured I'd hear a little extra noise but not as much as I'm hearing. it's a noisy gear sound. can't quite tell where it's coming from. Also the steering is pretty jittery when in 4hi...little bumps in the road bounce me all over the place. I tried going into 4low once and it kinda grinded a little...eventually went into 4low but then was almost impossible to get back to 2wd so never tried it again because I didn't want to mess anything up.

Also when I am in 4hi and try to go back to 2wd, sometimes it doesn't engage. Yesterday, for instance, I kept trying to get it to go back to 2wd, it wouldn't get out of 4hi...then I had to do a uturn in a cul de sac and in the middle of the turn it finally switched back over. Did turning have anything to do with it going back or was it probably just a coincidence?