I have a knocking (more of a thumping) that just started. When on the throttle I hear a thumping that speeds as speed increases but stops when I let off the throttle (even if I'm still rolling). Does not thump as I rev the engine, just as I am throttling up and down the road. It is coming from up front. Any ideas before I start breaking it down?

Almost like the driveshaft is hitting something as it turns.

 

Check to see if the heat shield under the hummer is smacking the drive shaft, just to rule that out.

 

Check your drive shaft, axle shafts, center diff mounts.

 

front prop shaft (drive shaft) CV joint at the rear of the shaft.
Check to see if the boot is torn or any grease around the area.

 

Did you ever figure out was causing the problem?

 

No....... he had the same number of posts as you did, 1. We do NOT dig up old Threads here. READ: Old Threads/'Necro-Bumping'

Ask your own new question in a New Thread.

First suggestion is to get under your truck and LOOK!