Its been doing this since I got it. after some long hard runs, when decellerating, i hear a gurgling sound coming from muffler, sounds like alot of unspent fuel boiling. or its extremely rich, maybe like the gas flow has not been shut off. but girgles or popping, is the best way to describe this sound. it almost sounds like it is going to die, yet doesnt, runs fine and it is not backfiring. i only notice this after hard driving.