[Skybird]

Psychological causes do not get aurally recorded on magnetic tape. As long as its not about the subject screaming.

Skip that medical and psychological stuff, the only things that may apply here are

- that humans may develope the sensibility for hearing this sound over ther life, with a climax in the age group 50-70, and then dropping again, meaning that after that that sensibility may decrease again;

- and that some humans can hear "electromagnetically", they can hear the Auroa Borealis and meteors in the ionosphere due to their electromagnetic signature that in any way may interact with the bioelectrically active part of the human body: nervous system, and brain. Some may even be able to "hear" radar, certain bands of it at least. It is not about accoustic but "electromagnetic listening". Accoustic wave travelling plays no role here.

This can lead to indeed the brain forming the idea of an accoustic sound - where there is no accoustic sound, but that idea nevertheless bases on external (electro magnetic) stimulus input. It is not a hallucination therefore, and also does not compare to tinnitus.

But when the hum gets recorded with microphones on tape, then it must be an accoustic phenomenon with waves travelling via the carrier medium of the air, same is true for the circumstance that repeatedly now me and my father noticed at the same time the Hum switching on or off when I was visiting my parents - they live on the other side of the city, 8-9 km in a straight line away.

No tinnitus. No paranoia. No hallucination and no collective hysteria. And my ears sharp and sensible and healthy like that of a lynx.

Personally I think that the hum is a label that must be understood to describe not just one but several possible manifestations of the phenomenon. Maybe it even are different phenomenons, I would not rule that out.