Got a 93 H1 that runs beautifully, no issues with temps and oil pressure reads good at all times. I have replaced all u-joints, center carrier bearing, alternator, all belts, all fluids, all glow plugs, all injectors. I had what I can hear as a chirp so I immediately thought alternator bearing or belts so replaced. Noise is still there. Noise does not occur if placed in Park and revving the engine at higher rpm. Noise occurs usually from a stand still and once I take off from a red light, it will chatter for a few seconds shifting from 1st to 2nd gear, then will go away if I let off on the pedal a little. I also tested if it is occurring, if I quickly shift into neutral when the noise starts, the noise will go away. It does not do it constantly, sometimes it will occur, sometimes it wont. Usually will occur when the Hummer has been driven for awhile (warm). I cant pinpoint the noise but it seems to be echoing from close to underneath me. Almost sounds like a heat shield bouncing off metal as the Hummer accelerates but I have looked into that as well and don't seem to have any issues there. Has anyone ever had any chatter issues that they could point me in the right direction? Thanks........... I do have a video but for some reason (probably because I am currently deployed and communications is limited) I am unable to upload it. I can send it through email.

 

thank you for sharing with us

 

Could be a number of things... I would check your rear drive shaft where it fits closely to the fuel tank there is a shield there that may be dragging, also do you have a vacuum pump? If so I would check that..