my h3t alpha has a very noticeable vibration in cabin at low idle in drive.
disappears when driving. I originally i believed it was coming from behind glovebox , now i feel its lower closer to floor.
please help,

 

What tires and wheels do you have and how many miles on those and how many miles on the truck.

When was the last time you hade the tires rotated and balanced?

 

hi. i have the 4 new michelin defender 20 inch tires on the hummer accessory 20 inch wheel. maybe 700 miles on wheels and tires, 97k on truck itself,

 

Post side view pictures of your tires/wheels showing the balance weights.
Btw, Michelin defender tires are NOT meant for alltime4wd off road!

 

Fellas, the OP says "very noticeable vibration in cabin at low idle in drive.
disappears when driving."

What the heck would the tire and wheel combo have to do with an idle in drive NOT MOVING issue?

OP:
Heat Shields - check them all!
Exhaust - possible loose or missing hanger
Motor Mounts - possible one or both are in need of replacement
Transmission mount - possibly worn and in need of replacement

What preventative maintenance have you performed on the Throttle body/plugs/wires/etc?
How many miles?

 

He did not say while stopped??? He said low idle in drive = idling down the road to me, ie. slow rolling, foot off the gas and moving, parking lot speed.....

 

i am having issue in drive gear but not moving

 

That would be a RATTLE!

 

Check your exhaust heat shields. There are stainless steel straps at several points along the exhaust that hold the heat shields in place and those straps eventually fail. The shields up by the CO2 sensors are also spot welded to the top of the exhaust just forward of the O2 sensor. That weld can fail and set up a nice vibration also. Sounds like a buzzing noise. Mine resonated around 1500 rpm. There’s another shield near the Y toward the back of the transfer case, and then one at the back where the exhaust goes up over the rear axle. Check them all! I found that tapping on exhaust components along the length of the system with a rubber mallet could replicate the buzzing, which helped me identify and isolate the broken spot welds.

Mine is now “fixed” with stainless steel hose clamps from NAPA, but O’Reilly has the same part for 1/2 the price. Hummerz will say it’s Jury Rigged. Lolz.

 

thank you all for the help !!