I have the same noise in a 2WD '01 Expy.

 

Supposedly, another cause could be the tcase clutches and the fix is replacing the tcase fluid. My 00 4x4 has 67k on it; I replaced the fluid with synth at 30k, and just did it again in May 06 at about 65k miles. The noise went away both times. My thinking is that that awd engaging through the tcase on demand must wear the fluid out fast. Try changing it with synth or at least make sure that's what gets put in with a new tcase. It might work.

 

I've used 4wd abt once since I've had mine. Would this still stand true? Even when I used it it was 4h or 4l.

 

Not that I am aware of. I think the AWD is running all the time; that tcase is always working according to the book. Which I think may put more stress on the internal gears, pinions, and clutches - to the point that one would have to change the tcase fluid more often than what the book says. Even I was reluctant to change it at 30k, but did it with synth and it ran quite for another 30k. Just my experience; others may have a different view. But, from what I can tell the awd runs all the time. I have used the manual 4h and 4l on occasion in the mountains or in snow, but very little.

 

Hey there MY's was doing the same and I thought that it could be my U joints, or Axles or wheel hub Bearing, But it was my Transfer case Fluid was really low and havent been change since the truck was made, I change it and Boom.....!!!!! No more noise, just check to see your level of fluids....

 

Hmm, must've been the reverse chain slapping that you heard. The fluid would dampen that noise.