Vibrations and noises are hard to diagnosise without being there.
Transfer Case. Check the fluid in the transfer case. I believe it takes a 18mm wrench to get the fill plug out. check for leaks. Also I found this info from GM
Also check the U-joints. They normally cause a squeak when take off.
#PIP4070A: Transfer Case Front Input Shaft Seal is Popped Out - keywords fluid grind growl inoperative leak noise - (Jan 25, 2008)
|Subject:||Transfer Case Front Input Shaft Seal is Popped Out|
|Models:||2003-2008 Chevrolet Express|
|Equipped with All Wheel Drive (AWD) |
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Technicians may find during any repair to the transfer case that the transfer case front input shaft seal is popped out and may be leaking. The cause may be due to a failed rear bushing and seizing of the propshaft slip yoke splines.
The front seal being popped out will be a result of this internal transfer case concern causing the slip yoke to overheat and bind resulting in the front input shaft seal popping out.
Tear down and inspect the transfer case, repair or replace the transfer case in the most cost effective way, replace the rear prop shaft slip yoke due to a possible binding concern and to prevent repeat repairs.
The transfer case fill recommendations have changed. Fill transfer case to the bottom of the fill plug. Add an additional 1.0L through the threaded speed sensor hole. The total fill amount is now approximately 2.5L.