I already run into trouble with the Jeep, (I thought you said that this was a good car..)
My rear diff sounds like its had better days, low speeds 10-20mph sounds like you are reversing with a normal car with manual gearbox.
At higher speeds it just howls, its not a broken sound but something is definitely going on.
I have Quadra trac II, just changed the oil but there was no difference.
I live in the far end of the world where taxes are high and these cars are rare.
There is basically no help to get. I found a full rear axle for a Jeep 2005 CRD Quadra drive II, will that fit on my Quadra Trac II? I guess not, next step is to find a repair-kit on ebay..