2004 Sharp Turn Chatter

Hello I recently bought a 2004 Liberty 4x4 w/ 48k miles. Here we are w/ the first snow and I've noticed it chatters and groans on tight turns or U turns in a parking lot etc...when in 4 wheel drive - and even a little in 2wd.

I'm new to Liberties so, is this normal? I was planning to change the oil in the transfer case. Can anyone tell me what kind of oil goes in there and is it difficult to change? I havn't even crawled under there yet... Thanks.