I'm gonna try my best to explain this. This is basically a phenomenon that usually occurs at certain points in the world, nobody has an actual name for this, however it's usually referred to as either Skyquakes (when a sonic boom like sound is reported to have happened in the sky) to "Worldwide Hums" (basically a name for most of the phenomenon's like these, but is usually referring to those low humming-type sounds), or even what I call "Sky Trumpets". What's very interesting is that not even scientists have a full on explanation on how these events happen, which means that all we have for explanations are just speculations. Said speculations differ, from an Atmospheric phenomenon with the Sun's rays messing up the Ozone Layer, to Power Lines/Power Plants causing these sounds, and people even say the United States Government's HAARP (High-frequency Active Auroral Research Program). Literally no one knows. All that matters is it really isn't that serious, sure it's creepy, but it's not gonna be the end of the world, despite what those conspiracy theorists say. I recommend researching this phenomenon, it's really interesting to look into, and it's pretty fun to look at the mysterious.
