thump when decelerating- 2000 LS2 w/79k

Has anyone else experienced a thump when decelerating a low speeds? it seems that the car will accelerate fine shifting through gears smoothly then I let off the gas and a thump occurs.. It feels to me like a bad mount somewhere and not directly related to the transmission. For a moment I even thought it came from the rear...

thanks, I look forward to hearing of your experiences, no uninformed theories please.

this is a universal dianostic chart you might want to look over.

http://www.saturnfans.com/photos/showphoto.php/photo/15886/

auto or manual trans?

is this right when you let off the gas or later at a certian speed range?

any difference in neutral?

LS2's only came with automatic transmissions and it ONLY happens when I let off the gas suddenly... I have experienced similar things in my Oldsmobile Bravada with AWD when the ball joints were bad..