...too complex to be a hoax? It was 15 minutes of looking up at the sky at nondescript locations while a sound got piped in eventually. That was incredibly easy to hoax. I could just find a shitty shakey cam video of someone bird watching or something, remove the audio, and pipe in odd drum beats or distortion sounds, then add back the original audio like the new sounds were part of all along. I mean throw in a strange shape or two or maybe some better indication of where the locations are, or maybe a few more people around and then we can start talking about a better video and more complex hoax.
I actually believe this now, I think I heard it a couple hours after posting in this thread. I took my camera out and recorded some strange sounds coming from the sky, it sounded like Ron Paul and he told me that he was creating invisible earthquakes all around the world that produces crazy interference with audio equipment on cameras. He told me that I need to believe, so now I do, and the earthquake's noise vibrations lifted me in the air. Also I took 2 tabs of acid. Don't try to debate me cuz I know it really happened.
My guess is that it's a hoax. A large portion of the clips have poor audio quality but the "sound" in question, is much higher quality. My point being most of these cameras being used simply lack the ability to record sound at high quality. Also, the sounds are mechanical in nature, so the shifting plates theory is pretty unlikely.