I love conspiracies, and am fully onboard with the notion that those strange humming/trumpet noises people have been hearing and capturing on video are the result of huge tunnel boring machines just doing their thing around/below their neighborhood.
For what purpose, who knows?
The more I research the more clues are revealed at just how key tunnels are on a worldwide scope.
Just to let you know, the picture of the TBM cutter head that you have is of the “Bertha” TBM in Seattle, 2013.
https://www.seattlepi.com/default/article/Mission-to-repair-Bertha-tunneler-hits-another-5651546.php
🐷