They do that when they want to go play in the mud. They get louder and also start whining if you ignore them... take him out on the trail... <img src="/forums/images/graemlins/wink.gif" alt="" />

My vote is the u-joints as well. Wiggle and rotate the driveshaft. If there is any play at all in it, they need to be replaced. If you haven't changed the fluid in the rear diff, transfer case and transmission, you may want to consider doing it as well.

Pmontero

'87 Montero Diesel
'98 Porsche Boxster Electric
and more...
Greasology
NotPetroleum