Oh, did I mention: at night, in an isolated area?
One of the problems with Hum research is that the answer may have already been found, but has been lost in the mists of time and obscurity. That will never happen again, as long as the internet exists and I am involved.
We should be able to find out if the worldwide Hum is an acoustic source. We simply need to send volunteers into a very high quality anechoic chamber and let them listen. We need the facility to be in an isolated area, however, because of the possible interference of infrasound from highway traffic or industrial activity. The experiment must happen at night.
I know that Apple, Samsung, Google, most governments and major universities, and many private laboratories have them. Our problem is that we are, as the Brits might say, “skint”. We may need to fund this on our own dime, perhaps with the goodwill of others who have the equipment and resources.
Let’s regroup: we are going to solve this, but “many hands make lighter work”. If you are connected to a facility that has such a chamber, find out if they are willing to help us.