Why is my computer making my music sound creepy?

So I’m just chillin listening to some music in itunes when all of a sudden I notice that the music is slower and sounds all deep and weird. It does this with songs on myspace and other places too.. and even the little shut down sound it makes is weird sounding. Usually when I restart it, I just goes back to normal but I was just wondering if this sort of thing has ever happened to anyone else? it doesn’t happen very often.. but I just have no idea why it does it in the first place. and my computer is a piece of crap windows xp if that helps.