The first and one of the most dangerous, problems with an exhaust system is a bad smell. When working, your muffler will funnel exhaust fumes outside and away from the vehicle. If there is a leak or other problem, those fumes could be stuck inside your car. This is the most dangerous problem because exhaust fumes can be fatal over time. If you smell anything out of place, make sure you bring it in to a mechanic as soon as possible.
The most obvious sign that your exhaust needs to be changed is a drastic change in the volume of your muffler. When working properly, the muffler should operate quietly in the background. When something goes wrong, it becomes a roaring monster. These loud noises are often telltale signs that you should have your exhaust system checked out by a mechanic.