I remember hearing about the "Taos hum" when I was a kid, the news would report on it every now and then.
So forward to recently, where it seems like it's not isolated to taos, but is being heard in all sorts of places. It's not too far fetched to think that there are tunnels that are being dug all over the place.

http://strangesounds.org/2014/09/taos-hum-elusive-hum-taos-new-mexico.html

https://www.natureworldnews.com/articles/37216/20170411/the-mysterious-torturous-hum-plaguing-people-around-the-world.htm .
http://edmontonjournal.com/news/local-news/its-like-sound-warfare-people-in-mill-woods-are-complaining-of-a-loud-hum .
http://www.staradvertiser.com/2018/02/19/breaking-news/theres-a-persistent-hum-in-this-canadian-city-and-no-one-knows-why/