Anyone else find that their concentration in zazen gets derailed by having a song stuck in your head? It happens to me all the time! I even stopped listening to my iPod for a month to see if that would help.
I have noticed though, that my personal soundtrack isn't so much influenced by the songs I've heard most recently. It seems to be an expression of my mood and current distractions (ie "Career Opportunities" when I was mad at my job, "Missing Words" when I was mad at my ex, etc). Which is a nice insight but it won't make it stop!