Ok so I had this posted on trailvoy.com and the Rodie told me to bring it here so here I am. My wife has a 2006 gmc envoy with about 80,000 miles on it. A couple of months ago it started to clunk when it was in a4wd. There is no noise at all until you get to about 25mph. You start to hear what sounds like road noise at 25mph to about 32 or 33mph. When you hit 34 or 35mph it clunks. Then the road noise goes away. It clunks again once you get to almost a complete stop. I replaced the transfer case because that was bad. I got one with about 40,000 miles on it. Replacing the tcase fixed the shifting into 4 low problem but the original problem "the clunk" is still there. I changed the front diff fluid and there was no metal in the fluid. The u joints and cv joints and wheel bearings all seem to be ok because there is no slop in any of them. It does NOT make any noise when it's in 2wd. I even took it to The gm dealer here and they are not sure and they don't want to start throwing parts at it if they don't need to be replaced. I need some help with this please because it's going to start snowing in the next couple of days and she is going to want 4wd. Thank you for your help.