The article features the investigations of science teacher and university lecturer Glen MacPherson, who, among other things, has created the formidable World Hum Map and Database an interactive website where users can register their encounters with the Hum. MacPherson believes that a scant 4% of humans are able to hear the Hum and has carried out numerous investigations as to what it might be.
Probably unsurprisingly for readers of Hummadruz, he can trace it to no single cause, and cites everything from freeway noise, through ventilation systems to blast furnaces as possible candidates. He does not mention fish. Ultimately, he concludes that the Hum is not based in any real world noise generation:
Rather, he argues it involves a neurological element
You will, of course, have already surmised that I am in accordance.