I just click sound off until the game starts

Which is a fine solution if the game starts soon, or if you have the MULE window in front where you can pay attention to it. It's much less useful as a workaround, though, if the game takes a long time to start (as they often do), and so you'd rather be able to put MULE in the background and do other things until it does. But turning the sound off means you can't hear when other players join the game.
For this reason, and also because when players go for break mid-game, the music loops endlessly, I'd really love the option to disable the MULE theme song (but not the other sounds) during the game. Or just make the song play once and then stop... there's pretty much no reason to have it loop endlessly. Nobody likes the tune THAT much!