Very cool! Incorporating the sung "happy little song" together with the static noise was very creative! Incorporating multiple sections representing different phases is nice. I wonder if it would've been cool if there was a build-up or transition to the fourth section, though this instant transition has its perks as well. Each section has its own aspect of the horror, just like in movies or games, which is wonderful.
Overall, really creative entry, I'll remember this one :D