What are those strange sounds being heard?

[Einstein2]

Talk about rock and rolling!

strangesoundsinthesky.com/category/earthquake-sounds/

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I did some research and found a sound on-line synthesizer that makes a noise sort of like what is heard in some of these videos.
So is some of this all just a trick or is it something really natural in the earth, doing with earth quakes or the outer atmosphere falling in ect?

[fbnstephen]

Whenever I see anything like this, my first thought is always: 'viral advertising'. One has to wonder if one of the upcoming 'end of the world' movies will be featuring such a noise.