wow i thought it was only 4 pages long...
well here goes:
It's a rural and quiet area of NY State called the "Catskills" which is legendary for having booms & rumblings heard by people even before the
American Colonies came into being...
the 'sky sounds' are described as being either a humm, or trumpets or booms or rolling thunders...
It seems that the 'sky noises' are spreading all across the USA and much of all the global northern hemisphere as well... (
We should investigate the smaller area called the 'Catskills' in NY State which has a reletively small area which had this phenomena going on for
hundreds of years.....
i would suggest someone should investigate this area to see if a reason or cause can be found for the source of that communities strange 'sky
noises' and see if we can apply that reason/cause to the rest of the nation and world where these mysterious sounds occur
i would cite the legend of rip van winkle as a source which acknowledges the actual existance of those mysterious booms/cannon thunder/ rumblings
almost everyday up in the rural Catskills in NY State
...Without exchanging words, the two hike up to an amphitheatre-like hollow in which Rip (van Winkle) discovers the source of previously-heard
thunderous noises: there is a group of other ornately-dressed, silent, bearded men who are playing nine-pins...
from wiki & the continuing reality of the all-too-unanswerable
Catskill Mountains... booms & rumblings
which were/are still heard even on clear days
i wish to add a few of my own "answers" to your OP List as to what may be causing the 'sky noises'
(f)... plants & trees.... yes... they do communicate,
the trees cry out from the clear-cutting type of tree 'harvesting'
(g) ...plants... the all too numberous fields of grain crops that get mangled for the creation of crop circles
are crying out in despair &
pain...it is only recently that crops have learned the frequency which humans hear
(h) ...UFOs are inter-dimensional craft, creating wormholes to enter & depart from our world...& when a portal slams shut we hear it
those are my three (3) personal favorite theories... the rest are not so substantial, so should not be shared... thank you