I'm not the kind of person that sings in waking life, not even along to songs playing.
But there has been times in lucid dreams. The only moments in my life where I felt such an intense sense of joy that I randomly broke out into song.
I remember one time having one of my lucid silly moments. And since I was so happy about being in lucid dream. I got a bunch of people in my dream singing. "If you're happy and you know it and you really want to show it, if you're happy and you know it clap your hands." And then of course, clapping hands.
Oh, I remember singing a made up song, I think. "If you're tough enough..." Something like that. Because I had used Telekinesis on a car and pulled the car towards me really fast like I was a powerful magnet. And just as the car was about to crash into me, I made my hand into a fist and punched the car really hard stopping it in it's tracks and smashing it with my fist.
Other than that I don't remember what songs I was singing. If it happens again, or I fond something I forgot about in my journal I'll pot it here.