A broken muffler may cause the car to have a louder sound than before. Thumping or clunking may indicate that something is broken in the exhaust system. Some mufflers contain baffles to reduce the noise of the exhaust system. These may become broken or loose and cause rattling in a muffler.

The benefits of an exhaust upgrade vary dramatically between vehicle models. Generally speaking though, less exhaust gas back pressure allows more exhaust gas flow, particularly at higher engine RPM.

Replacing your car’s muffler alone is not enough to open up the restrictive exhaust system and allow the extra airflow that increases performance. … MagnaFlow, an aftermarket exhaust manufacturer, says that its customers can expect horsepower gains of around 10 percent.

They should last at least 8-10 years unless you’re running really rich or something. Your catalytic converter needs to be replaced overtime but not the muffler. Like the muffler, it needs to be replaced when it starts leaking or if the OBD computers determine it is non-functional.