http://www.coasttocoastam.com/show/2016/11/23 , https://www.facebook.com/earthfilesnews
If some large tech is moving around the oceans, the general public will be the last to know.
http://www.cbc.ca/news/canada/north/ping-beep-hum-sound-arctic-ocean-igloolik-1.3831861
It could be intelligently controlled machines.
http://www.livescience.com/56759-mysterious-arctic-ping-investigation.html
Or, interplanetary vehicles poking around.
http://www.bbc.com/news/37875609
Perhaps even supplying deep sea and underground bases.
http://www.news.com.au/technology/environment/canadian-military-investigate-mysterious-sound-coming-from-arctic-seas/news-story/0262a19b08da9e1b1fce247f1e1d45ed
Some that might have been around since ancient times.
https://gizmodo.com/canadian-military-investigates-mysterious-pings-from-th-1788578162
Indeed, something might have been watching this world for a very long time.
http://www.newdawnmagazine.com/articles/enoch-the-watchers-the-real-story-of-angels-demons
Could the Watcher_(angel) be one of a class of sentient energy forms or inter-dimensional beings?
http://www.deliriumsrealm.com/watchers Various religions & myths can provide clues & hints about ancient history.
http://www.ancient-origins.net/human-origins-folklore/origins-human-beings-according-ancient-sumerian-texts The Earth could be someones laboratory experiment, school or prison.
http://www.crystalinks.com/libraryofalexandria.html
The Destruction_of_the_Library_of_Alexandria is a key point in time where a tremendous amount of data was lost.
http://www.biblicalarchaeology.org/daily/biblical-sites-places/biblical-archaeology-places/the-ancient-library-of-alexandria-
http://www.ancient-origins.net/ancient-places-africa-history-important-events/destruction-great-library-alexandria
Massive deep aquatic life forms are also something that the general public might never be informed of.
https://en.wikipedia.org/wiki/Bloop#Analysis
For many, its best to just consider the Bloop sound to be just another anomaly in the world.
http://www.pmel.noaa.gov/acoustics/sounds/bloop.html
http://weekinweird.com/2013/03/28/iceberg-unexplained-bloop-sound-worth-baffled/
http://www.wired.co.uk/article/bloop-mystery-not-solved-sort-of
https://io9.gizmodo.com/5962724/remember-that-scary-undersea-bloop-noise-at-last-we-know-what-caused-it
Officially, no one wants to say that ET life might have been around for more than the equivalent of a few billion years.
https://en.wikipedia.org/wiki/Wow!_signal
And that some of that ET life might have been watching & occasionally tinkering with this world & others for a very long time.
https://www.theguardian.com/science/across-the-universe/2016/apr/14/alien-wow-signal-could-be-explained-after-almost-40-years
http://www.space.com/33904-seti-mystery-signal-wow-alien-message-debate.html
https://www.earthfiles.com , https://www.youtube.com/user/Earthfiles , http://www.earthfiles333.com
So much of this world & universe remains a mystery but most people are too busy to notice.
http://www.ancient-origins.net/unexplained-phenomena
https://desertshapes.blogspot.com/search?q=ET
