geoff wrote:

It is known as The Hum, and there are all sorts of conspiracy
theories about it, from weapons research, government mind-control
beams, aliens, phantom planets, the Sun getting ready to implode,
electrical feilds, HARRP, gravity waves, etc, etc, etc. Most
adherents to those ideas radically HATE the idea of something as
mundane as (LF) tinnitus.

You obviously have you mind made up about whatever it was that you were
hearing and that everyone who differs must be a raving nutcase. But....

I had The Hum for years when I lived near Wolverhampton. An LF pulsing sound
that sounded like a large truck parked with its engine running. It started
soon after a large gas main was installed nearby and I could "hear" it in
and close to our house, especially at night. It sounded so real that I would
wonder around the house looking for the source. Nobody else could hear it.

I'm not sure it was tinnitus because I only ever heard it in/around the
house. It was so location specific. I recall pulling up onto our drive after
a completely hum-free holiday and turning off the car engine....immediately
I could hear The Hum. Since we have been living in Wales for the last 9
years I have never heard it.

I don't know what it is but I would not dismiss it out of hand as LF
tinnitus.