Stop in for a cup of coffee

Any of you guys ever run a car on jackstands to check the trans/gears... i got the exhasut on mine (still way too loud) and in second i have some noises that are like well.. i don't know how to describe it.. i'm wondering if the rear end having no load at all if the pinion could be bouncing off it's lash and making the driveshaft ring?

It's the metallic clatter you're talking about? I'm zero help here though....

@Mopar Tim