Is the Hum, a mysterious noise heard around the world, science or mass delusion?

I occasionally hear high pitched tinnitus, but usually only very briefly. Generally for me it is associated with worry/stress, and if I relax it immediately disappears (after a second or two). This kind of tinnitus that I occasionally hear just sounds like a high pitched whine, so I don't think it is related to blood flow or other body function. My guess is that it is just an overactivation of the limbic system.

Also, I just noticed that if I concentrate on listening, I can hear a fairly quiet high-piched tone. I assume this is just some background neural white noise signal. Normally it is not noticeable unless I consciously listen for it. I imagine it could get annoying or louder if I paid too much attention to it.

Another possibility it that it is just a kind of auditory hallucination that your brain generates when there is no other input, similar to closed-eye hallucinations:

https://en.wikipedia.org/wiki/Closed-eye_hallucination