What exactly causes the "Hum" near high voltage locations?

Factual Questions
1

I just walked by my office building’s power room. Lots of power cables in there and several switches and circuit breakers.

And the hum. VERY loud Hummmmmmmmmmmm, that id present in just about all such high voltage areas.

I recall another thread on a similar question a while that I wanted to go back to, but I couldn’t find it. So, at the risk of rehashing this question, what exactly si causing this sound?

2

Mains Hum and Corona discharge. Mechanical vibration due to 50/60hz AC frequency.

3

Here in beautiful Brook Park, OH we have a road that has one of those high voltage setups.

The way I remember the name of the road (Hummel Road) is associating that high voltage setup humming all day long!