Having a problem with your muffler? Fortunately or unfortunately the muffler might let you know when there is a problem, as well as the rest of the neighborhood.
If you hear a low pitch rumbling noise, there is a good chance your exhaust pipe has a hole in it or there maybe other problems with your muffler and exhaust system. Don't wait until it's dragging behind you. It may end up costing you a lot more if you wait too long.
You will also get better gas mileage when your muffler and exhaust system are working properly.