An ominous noise coming from the sky has alarmed people around the world - and experts have no idea what might be causing it.
Footage has flooded YouTube from locations as varied as British Columbia in Canada, Allen in Texas and Queensland in Australia.
The sound, like something from Hollywood movies The War of the Worlds or Close Encounters of the Third Kind starts without warning and has people transfixed in the street as it continues.
And even the experts can't tell if it's aliens, God, the Earth or something else unknown.
Chinese lanterns? ;-) To read more and view the video, click here.