It sounds like one of the U joints in one of your drive shafts. If you do not get the noise when at a standstill and revving but only when actually moving this is probably what it is. Many people refer to it as "angry sparrows". I had the same issue and it was the 2 U joints that are in the the front drive shaft in the joint closest to the transfer case. An easy way to check this is to remove the front drive shaft from the front Axel, tie it up well to the frame and take it for a drive in 2x4 if there is no noise you found the problem.