Wayne, when I bought my K&B .61 Twist it had a muffler very similar to yours except it had a plastic end cap on it. Inside it had a baffle that was held in place by a spring on the bolt. It appeared that the designer intended for the baffle to move rearward to make the expansion chamber larger as the throttle was increased. The spring was not very strong. The upshot was that the washer/baffle was wearing the bolt down and wearing out the hole in the baffle. When I heard it rattling I took a look. I replaced the spring with two pieces of K&S tubing locking the washer/baffle in place about halfway in its travel. Later MECOA upgraded the muffler with one with a metal end cap and a fixed baffle. I bought one for the Twist. My Twister came stock with the worlds loudest tuned pipe, I traded it to a feller in Fla. for the plastic end capped muffler.