I'm not talking about a musical improviser, someone playing live music often adds an underscore to every scene and can incorporate familiar music, but that isn't necessarily the purpose.
Still, in more serious long form improv, the inclusion of music that comments on the scene can often be more of a distraction than an improvement. A musical joke can cheapen some good scene work.
Our current sound improviser has really gotten the hang of short form, he's good at it, but we just started a run of unstructured Harold and he has made a few odd choices.
One recurring oddity was that he has played the Doctor Who theme song in about half the shows. I couldn't figure out why. We only loaded it on the computer for our Sci-Fi Theatresports night and it isn't familiar to most people in the US.
Friday night, I figured out why it comes up so often. Every time someone does a medical scene, he plays it. He's never seen the show Doctor Who, so he just assumes he's making a joke that other people understand. He thinks he's playing the equivalent of Marcus Welby or the theme to ER.
I do have to say, it was a treat to see a scene in a proctologist's office, from audience suggestion, with the Doctor Who theme playing behind it. I thought of the opening credits of the show with the TARDIS floating down an endless tunnel.