Thumping Noise

[88gt]

shifted belt in the tire can cause that thump

 

[adsm08]

I had the same thing happen and turned out to be a bad driver side u-joint

How do you get a driver's side u-joint when the d-shaft runs down the center of the truck?

Back to the OP

That is not a good noise. U-joint would be my first guess, but I'd also think that you could find it PDQ once you get under there and take a good look.

I heard of one once, same symptom it was a jeep, but same basic design underneath (trans, t-case, shaft, axle, etc) and it turned out to be a tree branch lodged between the axle and the body.

But I'd think that a close look should tell you what is wrong, anything making a noise as bad as what you described should be apparent pretty fast. It is something thats going to move in a way it shouldn't.