Have you checked the fluid in the differentials? Any signs they have leaked in the past.
I made some pictures/ diagram several years back, sort of when I was barely computer literate and had not long been a member. My choice of colors as well as the lighting had much to be desired.
Get on level ground (I prefer grass) Chock your wheels (front side and backside of one to prevent rollage in either direction)
Because this is a Liberty, you may not have room to crawl under. So you might have to do this on concrete using jack stands.
Back when, we'd just straddle a ditch or jump it up on to a curb. Regardless, chock and BE SAFE!
Now stick it in neutral so the transmission do not have it 'bound up"
Let's try my pictures now for what to check and how.
If they are too crude, let me know and I explain them.
But in the end, return here with your observations.
If indeed this is the issue you are having, you say yours hums, on my CJ-5 and Willys they will sort of quietly chirp when I let off of the gas and they are pushing (instead of being driven) I can catch the sound right off before they get worse.
Pictures below- your turn
Images (Click to enlarge)
Thursday, November 24th, 2016 AT 4:04 PM