system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: when its very quiet in a house or building, why do they tend to have a 'humming' sort of sound?
gpt
The electricity coming to a house or building is alternating current (AC), switching at a rate of 50 or 60 Hz. Typically, the range of human hearing goes as low as 20 Hz, so the frequency of the AC switching could be heard as a humming sound.