The Hum - Wikipedia
https://en.m.wikipedia.org/wiki/The_Hum
Check this out. I've been hearing it for years. So annoying
In response Dark Helmet to his Publication
Same, been hearing it for years intermittently. Becomes almost debilitating.
In response Johnny Five to his Publication
I use a floor fan at night to drown out the sound so I can sleep.
Occasionally I can feel the vibration from it. Very subtle. Therefore I think whatever it is moves. Cant tell what direction its coming from so its either coming from above or below.