How can I keep from singing

Driving without music is weird for me. Since my car radio is broken, I tend to sing a cappella a lot when I'm traveling. The oddest snippets of songs emerge out of the silence. Today, a few lines of an old hymn that happens to describe this urge to sing:

"My life flows on in endless song...
I hear the music ringing;
It finds an echo in my soul--
How can I keep from singing?"