[Steve Van Doorn]

Here is the sound amplified (this one has in the middle people talking softly in the next room. It gives you an idea how hard it is to hear:
https://www.youtube.com/watch?time_continue=18&v=ldQRMto1kIU

This was is greatly amplified:
https://youtu.be/PZSFI3vRabo?t=46

This is the sound of a nuclear reactor(my opinion on what it sounds like):
https://youtu.be/UxQdS0pbpKo?t=145

[PIF]

Thanks, but I hear it most every night in the winter here in WI.

[PIF]

And does not sound anything like the over amplified noise on those various recordings - at least to me. Perhaps the people making the recording have never heard the hum themselves and are just recording when someone else say to record. Don’t know. Speculation.

If you have ever heard a diesel engine running - albeit a bit rough - and listened closely for a few minutes - you can hear each cylinder firing, in this case there are occasional momentary lapses in the firing causing a rough sound before it resumes normal even firing.

Here (one of those dots on the WI map), the sound seems loudest when lying down and goes away when rising from bed. But just now, over or under I should say the noise of several hard drives spinning I can hear a low faint hum if I concentrate.