Your car's exhaust system and its muffler are very important to the overall performance of the car itself; the exhaust system helps to regulate how much oxygen and other fumes and emissions are in the engine, which is needed for it to create a healthy combustion. A muffler is so important for keeping your car quiet that in many areas, you can actually get a ticket for not having a muffler that's in good repair! Note how to diagnose a few common problems with a car's exhaust system and muffler so you can address these on your own or know what to expect from a mechanic.
Your car's exhaust system is mostly a long series of pipes that connect to the catalytic converter and the muffler itself. The muffler is typically connected by a type of hanger that holds it in place. If you hear rattling from the exhaust, this is often caused by a loose pipe or a loose hanger that holds the muffler. In turn, these pieces rattle against each other or rattle as air passes through them.
The best way to determine if it's the muffler's hangers or a pipe that is rattling is to determine where the rattling is coming from; if it's near the front of the car, this is usually a pipe, and if it's near the back of the car, this could be the muffler hanging loose. Check if you can easily tighten a connector to the pipes and the muffler hangers and note if this solves the rattling problem.
2. Muffler attached, but car is still noisy
If your car still has a muffler attached but is noisy, note if there is a lot of rust along the muffler and exhaust pipes. If so, the rust could have eaten a hole in the muffler somewhere that is not readily apparent. Rust along the pipes of the exhaust system can also create holes and if air is escaping out any of these, it's not making its way to the muffler to be quieted. You may be able to wrap some muffler tape around a hole in a pipe or the muffler and this might quiet the car.
Note too that sometimes the rust itself can cause a rough ride or for your car to seem noisy, simply because air is passing over the rusted surface and causing loud vibrations. If this is the case or if muffler tape doesn't sufficiently cover a hole in the pipes or muffler, you may need to simply replace them.