I have read a lot of posts about flyers having to replace their lost mufflers thaat fell out of the sky. I know that it happens. A flyer at our field didn't notice that his plane was getting noisy until I went to the flight line and told him. The engine was also starting to run rough. When he listened to the racket the plane was making, he landed it. Both bolts were almost completly out of the muffler. Another minute and I am sure that his muffler would have left the plane.