(Regarding a worldwide phenomenon called "the hum" )

I've heard The Hum for decades, since probably around the time the 1st HAARP arrays were installed--not sure; it varies pending geological formations, locations.
I toured Hoover Dam as a child, hearing /feeling the vibrations / sounds from the huge generators inside that, and being brought up around electrical equipment, I'd describe it VERY similar to the sample.
The Hum I hear sounds exactly like a huge electrical generator motor operating at baseline RPM's, while vacillating up / down, in patterns that could be coded message sendings--not Morse Code, but along those lines. I believe there is messaging over that system, because during times of politically charged events, when the US Gov't is getting away with something, activity wildly increases--as it did during about 2-3 days prior to 9-11. Then, for the 1st and ONLY time I EVER heard that system totally shut down, The Hum suddenly stopped completely, for nearly 24 hrs, immediately following 9-11.
When it resumed, it was EXACTLY like a huge electrical generator slowly winding up to operating RPM's, then commencing low-key vacillations of messaging over that system.
The Hum differs from other sources of sound/vibrations; I can sort these out pretty well, isolating most.
NOTHING I've found, has been able to shield against / modify The Hum; Power outages help, only by reducing total load.