The noise has been narrowed down to one island that has "a few blasting operations". So stop the operations and see if the hum goes away. Then have each one restart one at a time. Or bo binary search, whatever. It doesn't matter.

The obvious takeaway here is that the city/state/province does not care. They are too deep in the pockets of those industries to make any waves at all.

Government has so little power to do anything. They are just the paid legitimizers of the corporations.