Driveshaft Noise 2005 Chevy Uplander

When I step on gas from stop, a little mild clunk from underneath sounds like the rear end (universal joint), but when I’m very gradually press the gas pedal from a stop, it doesn’t make a sound

Sounds like a good time to inspect. I would place the rear two wheels off the ground on jack stands on a level surface. Chalk the front wheels and place the transmission into neutral. Crawl underneath and while holding the rear differential pinion shaft with one hand and the center of the driveshaft in the other, check for play. And listen for any noise etc. Might also be a good time to check your rear end fluid level. You may want to change the fluid to fully inspect it for metal flakes in the fluid. Here is a video of my 2006 Chevy Silverado rear end fluid change to give you an idea of what is involved.

DRIVESHAFT, REPLACE

1. Raise and support vehicle using a suitable lift.
2. Reference mark propeller shaft at transfer case flange.
3. Remove propeller shaft-to-transfer case flange bolts.
4. Reference mark propeller shaft at torque tube flange.
5. Remove propeller shaft-to-torque tube flange bolts.
6. Push propeller shaft toward rear of vehicle.
7. Remove propeller shaft.
8. Reverse procedure to install, noting the following:
   a. Torque rear propeller shaft to torque tube bolts in a cross sequence to 24 ft. lbs.
   b. Torque rear propeller shaft-to-transfer case flange bolts to 24 ft. lbs.