My muffler is rattling and it's worse when my AC is on. My husband went out and checked it today and he told me that there is something inside of my muffler rattling around. Could something have fallen off inside the muffler that was once attached or do you think it's more likely to be a rock, stick, etc.? Mind you, he knows nothing about cars so if you have any other ideas about what it could be please feel free to include them. Thanks!