I always have loved a good mystery.
They are being called creepy, spooky, strange and just about every other adjective that can be used for something unexplained and these strange hornlike sounds are being heard across the world. Explanations range from natural phenomenon to Apocalyptic, biblical omens to magnetic fields.
They seem to be almost musical in nature, for lack of a better description, and have been likened to the sound of trumpets. Many think they could be hoaxes, and no doubt some could be, but they are heard in different countries, different locations within those countries, uploaded by multiple different users and all are similar sounding.
The videos below are a small sample of what can be found searching for these strange sounds coming from the sky, including video compilations of sounds spanning the globe, going back to 2011.
Last but not least, a video titled "The Hidden Truth - Strange And Unexplained Horn-Like Sounds Filling The Air 2012"