I've been having a nightmarish time trying to track down intermittent low frequency industrial noise.

It's over the EPA regulations, it's neighborhood wide, and it is on for 2 hours between 11pm and 1am on random days. The EPA did monitoring of the house and site but couldn't pinpoint where it was coming from because of how low frequency it was.

This isn't surveillance, this is the equivalent of finding who is dumping raw sewage in your drinking water.