Strange Sounds Echoing Round the World - What Are They?

These "strange sounds heard round the world" series of YouTube videos is a strange phenomena.  I must say I find the sounds to be extremely hypnotic and relaxing.  The video compilation below was posted just two days ago having gone viral with nearly a half a million views.

YouTuber Dutchsinse posted the video with this info:

"Something strange is afoot --- unknown sounds heard globally over the past few days.. basically starting up in rapid pace on January 11, 2012 --- up until today (jan 16 2012). I don't know how long this will continue, or what it is. New term : U.A.O.. = Unidentified AUDIBLE Object you can see all the same videos in this montage by clicking this search here: http://www.youtube.com/results?search_query=strange+sound... What could all these sounds heard this past week around the world have come from? What do you think is causing this phenomenon? I am still at the drawing board, trying to figure this mystery out... any ideas.. please share below in the comment field." - Dutchsinse Channel Video Link

My idea is that they sound like whale mating call recordings blasted on loud speakers,  that it's some kind of hoax to get YouTubers to react to worldwide.  The cause would likely be to bring attention to Navy abuse of whales.  Then again, they don't always sound like whales either.  They could probably put it all on a CD unknown artist compilation and sell it on iTunes under "Sounds Heard Round the World".

YouTuber TrutherGirls's take on the video asks if they are the "Trumpets of Revelation?"  Not one of her better videos, but still interesting nonetheless.