Underground Bases, Electromagnetics and Plasma
Two events are relative to these sounds. They are the construction and demolition of underground spaces as part of the underground base operations. The other is the accumulation of magnetic fields in the atmosphere and the resulting ‘electromagnetic’ speaker effect of intersecting fields of energy.
Underground Base Construction/Demolition
Some of the equipment used for the creation of the underground bases are capable of shaking the ground for miles. Explosive devices are sometimes used and house sized drills and construction devices are used to crumble and move the dirt and rock. Some sounds are possibly related to this, but for the continent wide hearing of sounds the below explanation is probably more relevant.
Electromagnetic Sound Generation
These videos demonstrate how organized sound can be generated through the occurrence of electrical arcs. The arcs themselves are creating the pattern for the sound waves through the air.
Now this video, whether copied or not, contains the same strange sounds. What if the electrical impulses were not that of music, but that of increasing or decreasing tones and harmonies? We would ultimately get a “song” made out of the ringing of electromagnetic fields and the effect of these fields on the air around the points of intersection.
This sound would be the same effect just at a much lower frequency and across a larger space.
Recreating Through Electromagnetics and Plasma Fields
It fairly easy to imagine what this would sound like if you extrapolate from the videos above involving sparks and music. Very low frequency waves across a very large platform would generate the corresponding very low tones that are heard as sound.
We are experiencing an increase of energetic phenomena and the creation of plasma fields and this is through natural and artificial means.