Not to be a party pooper, but frankly I have to say that I consider these videos to be a straight up hoax.
a number of video and audio-only recordings have surfaced which purport to be strange sounds coming from the sky. In some videos the sound is just a hum that seems to come from everywhere at once. In others, the sound is metallic, or groaning. Some people hear a noise that resembles human screams (similar to those heard in the "Siberian hole to Hell" hoax from many years ago).
What is going on?
There are a number of possible theories. Although not to be a party pooper, but frankly I have to say that I consider these videos to be a straight up hoax. Crop circles for the internet age, if you will.
Whether it's an early attempt at viral marketing or just a series of people who decide to pull a prank on the world, I'm not sure. I also can't put my finger on what about these videos trips my "fake" flags. It's just instinct on my part. Something about the quality of the videos, the fact that the noise is seemingly only recorded by one person in the entire country, and the noises themselves… it all screams "hoax" to me.
Anyway! Other theories include:
The all-purpose sky villain. Could the HAARP antenna array in Alaska be somehow activating the atmosphere, strumming the sky like its own, well, harp? The sky hum does seem to have an electrical component to the noise.
Similarly, solar flares could theoretically be galvanizing the sky in a way that releases energy into the audible spectrum. An auditory version of the Northern Lights, in other words.
The global nature of the noises, which have been reported in Canada, Bucharest, and Kiev among other locations, makes some people suspect a geologic source. Could this be the sound of the Earth's tectonic plates shifting around? Could it be the precursor to a massive earthquake? Or just a sort of geologic burp? The phenomenon of earthquake lights is fairly well documented; could this be an audible version?
Well, it's 2012, so you know a certain segment of the population is going to blame the Mayans for this, or whatever. Could this be the horn of Gabriel calling Earth's souls up into Heaven? And if so, why has no one been Raptured? (Is it possible that we ALL failed the test?)
Many of the sky noises closely resemble the sounds of a distant jet engine. Could this be the work of a high-flying experimental military plane?