if this is the wrong area to post this move it. the truck in my sig. has the cat with open exhaust into stacks. when it's at idle it goes from a deep rumble to a hush mode like it keeps switching from a muffler to open exhaust. what is it? does anyone elses do that? is it only on the LBZ?

http://dieselplace.com/forum/showthread.php?t=30812&highlight=exhaust+tone+changing

AAAHHH my search should have said exhaust tone. thank you