[jimmytidey]

No doubt engine noise is caused by lots of factors. You can modify they exhaust to make it louder or quieter. I understand a lot of bikers modify their exhaust to make it louder.

As I understand it, there is a legal limit on noise emissions some for vehicles. To get round this bikes are supplied with a quiet exhaust and a second loud exhaust. They tell customers the loud exhaust is for use on private race tracks but obviously this is widely ignored.