Front U-Joint problem?

[pugsy]

92 XLT 4x4 with auto hubs. Was out driving in the snow tonight. The 4x4 works great, awesome traction in the snow. When I have my foot on the gas, it drives fine and no noise or vibration, but as soon as I let off the gas, I get a intermitten grinding/clunking coming from what I think is the front left wheel. Almost sounds like when the autohub is buckling, but the hubs are grabbing fine and I have power to all 4 wheels. Could this be a bad u-joint? It is pretty rusty when looking at it.
Is it hard to replace? Or would a shop charge an arm and a leg to fix one side?

 

[nismotunedgtr]

I noticed the same thing the other day using my 4x4.

 

[cculter]

My guess is on the front u-joints, if it were the hubs they would clunk when on the gas. When youlet off the pedal there is no tension on the u-joints and they can move around. The joints are easy to change, there are a few threads on here somewhere that can help you take apart the front hubs. Very inexpensive fix. Good luck