People have been reporting a mysterious Hum for decades. Looking back through the History of the Hum eliminates some of the causes that have been suggested for example 5G and Smart Meters.

The oldest news story about the Hum confirms reports by a considerable number of people in the UK in 1977 which is 46 years ago. I am still searching for news stories or documentation of any kind that confirms the existence of the Hum prior to this Date.
 
46 years ago

1977 - "The Mirror" a Newspaper in the UK  ran an editorial titled 'Have You Heard The Hum?
https://www.edinburghlive.co.uk/news/edinburgh-news/mystery-roslin-hum-maddening-sound-16269447

29 years ago

1994 - Hugh Witherington in Peterborough United Kingdom reports hearing the Hum
https://www.independent.co.uk/life-style/what-s-that-terrible-noise-all-over-the-country-people-are-plagued-by-a-strange-hum-are-their-ears-playing-up-or-is-it-something-sinister-emma-brooker-investigates-1424317.html

22 years ago

2002 The Vancouver Hum - Mysterious ‘Hum’ Harasses Vancouver Residents - By Mark Stevenson - CTV Environment Reporter - 10-6-2002
https://emrabc.ca/?p=3950

11 years ago

2012 - Glen McPherson reports hearing the Hum for the first time near his home in Sechelt, British Columbia
https://apnews.com/article/a442037fb3114fa28d46894d9eb2ac68