The electric buzz, without the shock
Mains' hum or electric hum is a sound associated with alternating current at the frequency of the mains' electricity. Electric hum has 60 Hz fundamental frequency in the US or 50 Hz in the EU, and a lot of harmonic content above. The fundamental frequency creates the hum (the brown slider), and harmonics create the buzz (the other sliders, the blue and purple in particular).
This noise came from a user's request, associated with a particular experience. Jenny writes:
"You are sitting at school and while the teacher blabs away about stuff you don't really care about, you stare up at the ceiling and get lost in the sound of the light. It buzzes in a medium monotone and it almost sounds like a fly or bee buzzing around. But it's a light and it makes you feel more comfortable than a bug. You know that some street lights do this as well, in different tones with each one. This is why you sometimes spend the day at a friend's, and walk home at night. You love this sound so much and sometimes you wish you could hear it all the time."
Don't forget to turn off the lights when leaving the room, Jenny.