There is something loose on the bottom of the car that drags on the ground over bumpy areas.
Hi. You should have this inspected soon as there could be costly damage as a result. Over time the mounts that hold the exhaust system and muffler can become loose allowing them to swing around or drop lower than intended. Even if its just the plastic shroud hanging down, it should be mounted back up. If the shroud were to be ripped off while driving, rocks and other pieces of debris would be able to get up inside the engine bay possibly causing damage to other components. Have a certified technician, such as one from YourMechanic, inspect the noise and look for signs of damage.