Question

Why sometime a loud sound release through silencer?

Answer 1

The sound is due to misfire in cylinder.

Some old bikes make that type of sound when we run it, Because of the carbon deposit in cylinder head or due to carbon deposited on spark plug pin which results in sometimes misfire or may be due to irregular fuel supply by the nozzle of carburetor.

The pop sound / firing sound on bullet is due to missing of spark. People switch of the ignition and turn it on which results in ignition of the fuel which is not ignited in last stroke. It cause deposit of more carbon plus it harm the cylinder of bike. People think that it's kinda cool but it's not, neither for us nor for bike.