It's the whole shaft moving up-down.

From reading other threds I now know that I have been running the engine hot most of the time, which I'm sure have contributed to this.

Do you have recomendations for another muffler to get? This is my second evolution muffler and I'm very unhappy with it.

The engine still seems to run fine i.e. lots of power etc., but the noise bugs me and just doesn't feel right. If changing the bearings will fix this, It's worth a try. I saw that replacement bearings from Horizon hobby are running about $9 a piece.

Tycho