Why does my bike create a loud explosion like noise from the exhaust pipe (Silencer) occasionally?

There should be general checking done as per normal routine....good tuning , cleaning of all spark plugs, timing .....there are vital. If any of these are lacking , there is usually some 'misfire or backfire' , which does affect the engine and the performance of the vehicle in general. Some people switch off the engine and suddenly start the engine by putting the vehicle in gears......that is also a possible cause of such sound of explosion......don't practice or try it ....it's bad .