In January of 2012, certain areas around the world began hearing strange, loud noises more and more frequently. It would cover a large area, and for the most part sound like a thumping, whooshing sound, that is rather atmospheric and difficult to describe with mere words. This was more likley heard in dark caves and chambers.
Some may have seen the news report, on a local American News channel, and the sounds are explained by experts there. The worlds magnetic poles are getting more and more repellent, as these two poles move away, it generates a lot of electromagnetic noise. At least, this was the one of the many explanations experts gave us.
I'm not one to believe in conspiracies, though.
However, in one recorded case in the state of Colorado, USA. The sounds were heard by two hikers. This was the only case where the sound was... different. The sound would get louder, as if it were approaching the camera operator about halfway through the video that was posted on YouTube. As the video started to finish, the noise was noticeably quieter and further away.
This provides a theory that something was moving. This 'something', if it were in the sky, we would be able to see it. So whatever it is, could be lurking underground, and able to move very quickly; after all, the sound spread from Mexico to England, within an hour.