any ideas??
 

not sure how to describe this but here goes...
saw a truck today go thru town with the oddest sound exhaust. it SNAPPED when he let out of the gas......... followed it thru town and it was very loud. at stop lights he would rap the throttle and that thing was quick to spool and like i said it had a SNAP to it!! so any ideas what he might have had going on there?????