In late 2011, residents of Windsor, Ontario, South of Detroit, MI, began reporting a low droning vibration.
Sometimes loud enough to be irritating.
One evening in 2012 saw 22,000 reports to officials.
It was estimated that the sound was emanating from Zug Island, a heavily industrialized section of River Rouge on the North bank of the Detroit River, which separates Windsor & Detroit.
Canadian officials requested U.S. assistance in determining the source.
But local authorities were stymied by official refusals to allow access to the island.
A steel mill operated by U.S. Steel was the possible cause, but officials stated that no new equipment had been installed or activated around the time that the noise became noticeable.
When the blast furnaces were deactivated in April 2020, the noise went away as well.