If you don't let all the way off the thottle when ya decell, unburned gas builds up in the exhaust and "pops". It did it before probably but ya didn't hear it when ya had the mufflers on. I can make mine do it or not, depends on how I ride. I usually let one off when my wife gets too relaxed. Makes her jump every time
Ride it
O0It won't hurt a thing
