Occam suggests that the sounds are either able to be explained as typical noises that 'just happen' or are hoaxes. It is unfortunately extremely common for a large number of copy-cat reports of major "strangenesses" to occur once something suitably notable appears "on the web".
There are numerous web discussions about these "phenomena".
This 14 minute video does a good job of covering the above points. Below I've summarised his points but if you are interested in ythe subject thr video is worth seeing. His approach is reasonable and logical - this does not make him right, but ois a better than usual approach.
Firstly he demonstrates, with a degree of detail that allows anyone to easily check what he says, that many of the videos are hoaxes, and many clearly use copies of parts of the sound from an early and so far unexplained. ,
Next he demonstrates the proven everyday source of some of the sounds which were recorded and reported by others as examples of "strange sounds from the sky". A good example is an amazingly impressive "celestial chorus" generated by a bulldozer with blade down being used to scrape roughnesses off new concrete at a skate board par.
He then explains typical mechanisms that might explain otherwise unexplained phenomenom.
Finally - some such sounds may have highly esoteric sources - but it does not seem likely that this is in fact the case given the probable alternatives.