Strange Sounds from the sky captured over California (USA), Minneapolis (USA) and Southampton (UK) and nobody knows why

Strange Sounds from the sky captured over California (USA), Minneapolis (USA) and Southampton (UK) and nobody knows why
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Strange Sounds

The strange sounds from the sky are back again. They were recorded in May in California, Minnesota and Southampton.
Strange Sounds May 2018
A mysterious noise from the sky is continuing to baffle people all over the world – as well as giving those who hear it sleepless nights. Sounding like a trumpet or a collective from a brass section of an orchestra, a selection of videos shot from the Canada to Ukraine, via the U.S., Germany and Belarus show strange goings on above us. And the eerie sounds have been continuously heard at all different times and locations for almost a decade.
More lately the sounds were captured over Bellflower, California on May 11, 2018:



https://youtu.be/73Ric1Xe4A8

over Minneapolis on May 14, 2018:



https://youtu.be/z6uKsQO2I5Y

and over Southampton (UK) April 30, 2018:



https://youtu.be/71vqgZryVEw

What people are speculating the sounds are online… Possible theories include:

Tectonic plates grinding – Tectonic plates are pieces of the Earth’s crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km (62 mi) thick and consist of two principal types of material: oceanic crust (also called sima from silicon and magnesium) and continental crust (sial from silicon and aluminium).
Atmospheric pressure – Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air above that surface.
Trains shunting – Self explanatory – noise comes from trains in reaction to the track and overhead wires.
Construction – Building works, especially if going on at the same time across a specific area, can led to similar sounds.
Aliens – Can this be an alien lifeform in the sky, perhaps scouring out Earth?
HAARP weapon – Rumours persist that the U.S. government uses secret weapons in the sky for defence and weather modifying, the High Frequency Active Auroral Research Program (HAARP). This wouldn’t explain the sounds in other countries however…
The Apocalypse and the Seven Trumpets of Heaven – Seven trumpets are sounded, one at a time, to cue apocalyptic events that were seen in the vision of the Revelation of Christ Jesus, by John of Patmos. Somewhat more worrying as it would signal the end of the world…
What do you think those are?

Thanks to: http://strangesounds.org