The exhaust system expels fumes away from the engine. These fumes are sent through the catalytic converter, into the muffler, and expelled outside. Signs of exhaust issues include hissing/tapping noises while accelerating, the car not accelerating properly, strange smells coming from the car (burning smell is caused by exhaust gases leaking into the engine bay and burning wiring/plastics, for example), vibrations (in the brake pedal or steering wheel), hanging/dragging exhaust pipe, abnormal exhaust smoke (too much smoke or blue, black, grey, or white smoke), rust, and decreased fuel efficiency, for example.