The Rebel 1100 stock muffler has two muffler sections – you can drill out each baffle with a drill extension. Start with a 1/2 inch hole. If it is not loud enough, use a larger drill bit.
A guy in a FB group did it and he says it sounds much better. He punched his out with a sharpened metal rod and hammer – the hole looks like 3/4 inch or more.
Rebel500 