The muffler in car plays an important role in lowering the volume of noise generated from the exhaust system and also helps in keeping the exhaust system in place. Normally due to their functioning, the occupants of the car are not aware of the noise coming from them. However, any abnormal noise from the system indicates that there might be a problem like a hole in the muffler. Go through the slide to the ways to recognize a hole in the muffler of your car.
http://www.slideboom.com/presentations/2179687/How-Could-you-Recognize-the-Hole-in-the-Car-Muffler