The muffler for a motorized vehicle includes a housing with an inlet chamber and an outlet chamber, an exhaust inlet, and an exhaust outlet. The muffler includes a first channel with a first noise dampening amount that is within the housing interior, to fluidly connect the inlet chamber and the outlet chamber. The muffler includes second channel with a second noise dampening amount that is within the housing interior between the inlet chamber and the outlet chamber. The first noise dampening amount is greater than the second noise dampening amount. A valve selectively fluidly connects the inlet chamber and the outlet chamber thorough the second channel, and is configured to variably obstruct the flow of exhaust gas through the second channel. In various embodiments, the muffler has more than one inlet chamber and more than one exhaust outlet.