Apparently Billy Joel is haunted by fans or some other demons of the night as this "backmasked" song shows. If you play "We Didn't Start the Fire" backwards, you will hear the words "Get out of our sleep". Nice.

I've provided audio snippets below so you can try it out for yourself.

Song: We Didn't Start the Fire - by Billy Joel
Snippet:
Regular Lyrics: We didn't start the fire
Reversed Lyrics: Get out of our sleep
Download regular audio snippet here
Download reversed audio snippet here