Hello and thank you for using Justanswer. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.
Is it a single clunk when accelerating?
yes its a single clunk, it happens frequently when moving off from a stop line or when i would suddenly accelerate
The common problem with the H2 is the body mount bushings popping. The fix is to install insulators between the body mount bushings and the frame.
Bulletin No.: 07-08-61-006CDate: July 24, 2008Subject: EI07118 - Underbody Noise, Pop, Creak, Body Mount (Install Upper Body Mount Insulators)Models:2005-2008 HUMMER H2Supercede:This bulletin is being revised to adjust the labor time. Please discard Corporate Bulletin Number 07-08-61-006B (Section 08 - Body and Accessories).ConditionSome customers may comment on a noise coming from the underbody of the vehicle.CauseThis condition may be due to body coning in the area of the upper body mounts.Correction
Install insulators to the upper body mounts.
i said that i have a H3 and NOT a H2
do you think that the front propeller shaft universal joint could be a source of a problem; my mechanic said it is broken and needs replacing
When universal joints break, the driveshaft will fall down on one end. If the driveshaft is not hanging down, the u joint is not completely broken. The u joints can fail and have a good bit of play in them and make a clunk noise. If the u joint is worn, I would definitely address this first.