Happy Birthday?

O.K. so there are trucks here that will come every few days or so and they spray the roads with water (I’m guessing to clean them). As they drive through, they blast the Happy Birthday song (without words), we’re on the fourth floor and it sounds like they’re in the next room when they drive by. Anyways one morning the Happy Birthday truck was making it’s rounds and Sydney turns to Heather and says “Happy Birthday Mommy”. Not only was this funny, but it was cool to us that Sydney knew what song it was even though there weren’t any words.