MOVIEGOD over at GEEKSOFDOOM.com has postulated that the supposed strange sounds being heard and recorded all over the planet are really just the fledgling stages of a soon to be marketing campaign for the new Godzilla movie. Now personally, unless it's a Polaroid, I don't trust anything I see (or hear) on film. So I think this guy is on the right track. Hit the link to read his theory and listen to the strange creepy sounds.
Strange Sounds Heard Worldwide: Is It Viral Marketing For ‘Godzilla,’ ‘Cloverfield 2,’ Or Something Else?