I have the .36 and it did the same thing. There is a small silicone gastket between the two parts of the muffler and this wears out with time. As the exhuast builds up heat when the engine runs, the bolt in the exhaust grows a bit and the back end of the muffler rotates as a result of the natural vibration of the engine. All I did was to put some teflon plumbers tape around the flange of the muffler to create a new seal. Also, run the engine up to operating temperature and then tighten the bolt.This will stop the back-end of the exhuast from turning.

Hope this is helpfull.
Good luck