Clunking help

Ok I need some ideas on what could be wrong with my Heep. I clearly broke something the last time I took out the XJ. I can only take the it about 20mph before I start hearing this nasty clunking up front. (Reminds me of putting a baseball card on the spokes of a bicycle) I have tried pulling the tires and rotors and cleaning up the around the wheel bearings and breaks in case there was caked up crap in there...I checked the fluid in the front diff and it is probably a half inch below the filler cap. I thought I might have eaten up my gears but I didn't find any metal shavings floating around in the gear oil. The noise is clearly coming from the front and gets worse the faster I go. There is a slight vibe along with the noise. It happens in 4wd, 2wd, and in neutral. Any ideas on what else I should be looking at? Could I have damaged an axle shaft? This is driving me nuts.

If I lift the XJ on stands and spin the tires, I don't hear any sort of noise from the bearings or diff. I don't get it.

My front wheel bearings, and ball joints are damn near brand new. Probably 3 months old so I doubt they are the problem. Please help,

Take a good long hard look at the axle u-joints. Sounds to me that you've named all of the best symptoms!

I got under the XJ and noticed that I have about a 1/2" of play in the front driveshaft. I can grab it and turn it easily by hand about a 1/2" in either direction. The rear DS is solid and has no play in it.