In recent months there have been a number of YouTube videos posted from around the world of unusual sounds emanating from either the ground or sky, with no clear point of origin. Videos have been posted from the United States, Canada, Brazil, Costa Rica, Budapest, Taipei, Chile, Mexico, Czech Republic, France, Norway and Denmark.

The sounds can be grouped into a few different types, the most common being a low roaring or metallic sound that has been compared to the sound of the tripods from Speilberg's War of the Worlds, or to the monster from the Cloverfield movie. Other sounds are a low throbbing and a vocal-sounding reverberation. Some names being used are "Godzilla" or "apocalypse" sounds.
In November 2011, Macleans magazine ran an article about a low humming that was keeping residents of Windsor, Ontario up at night.
In January, television news in Costa Rica ran a story about these sounds, and several YouTube videos have been posted from Costa Rica.
In the past week, a wave of reports have come in from western Canada, including this video from an Alberta forest.

What is most remarkable is the consistency of the sounds across different regions of the globe.
Not surprisingly, many theories are being put forth, such as biblical apocalypse, HAARP, Mayan calendar, and military testing. Another idea being talked about is that this is a meticulously executed marketing campaign for an upcoming movie or video game. Out of the large number posted, some videos are clearly hoaxes.