system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do power lines buzz?

Out on an essential walk and I just walked under some power lines, why do they make that loud buzzing sound?  Thank you!
gpt
Some power lines have pretty high voltage. It can be enough to cause corona discharges. They happen when the air ionizes and conducts current. Think of them as brief mini-lightnings. The sound is like a very weak but continuous thunder.

In transformers a reason is also because switching magnetic fields vibrate the components.