What are these bizarre sounds coming from the sky in countries from Hungary to Canada?

What exactly are we hearing in these YouTube videos posted by people who claim they've recorded ear-splitting roars coming from the sky with no explanation? Here you can see one of the latest, recorded in Budapest, Hungary last week. Conspiracy-lovers are calling them "apocalyptic sounds." Whatever they really are,… »1/16/12 10:40am1/16/12 10:40am