Maybe it was just a fluke. I only heard it once, it was kinda cool actually. We had just returned from a trip and while the family was piling out, I revved alittle(1500?), and heard a douple pop from the muffler area when the engine was deceling. Of course I tried it again and it didn't happen. Maybe it was just the muffler cooling off, but it definately sounded like a slight back fire or the pop and crackle you get sometimes when the exhaust is loaded with some unburnt fuel. Oh well.