Short distance high rev run cause lots of exhaust popping

[Roper_imp]

Is the aftermarket exhaust a full system or a slip-on? Check the connections. Decel popping is caused by unburnt fuel detonating in the exhaust. This can happen when there's an air leak. When outside air enters the exhaust, it's like blowing on a hot coal--it will ignite. When you ride for longer, perhaps the hot metal has expanded enough to seal the leak. On shorter rides, there's still enough of a gap for air to get in. Check all the joins. There are many online tutorials for sealing gaps in exhaust systems. Gorilla Glue is not recommended!