Mufflers are part of the exhaust system. This system routes dangerous gas from the engine out and away from our vehicles. It also reduces exhaust noise.
When the exhaust gets noisy, we automatically assume it is the muffler, but this is not necessarily so. There is also O2 (oxygen) sensors, catalytic converter(s), exhaust pipe, resonator and a tail pipe that could be the culprit.
Keep an eye on the exhaust system if you hear noises when starting, accelerating or braking.