I've had many lucids and nonlucids with background music. Most of the time, i didnt really conjure them, they just played by themselves. And I even remembered the lyrics even when I was sure I had forgotten them. I only managed to actually conjure the music twice in different lucids. In one, I just imagined a song I know to start playing and at first it was hard to summon the first melodies but after it started, it went through on its own. The second one, zi used a dream radio to help make the summoning easier (easier to use props than pulling it out of thin air :p)