Here is a fascinating random Internet find. Wikipedia has a “List of unexplained sounds”. They are sounds that have been recorded in various circiumstances that can’t be attributed to any human, bigological or geological activity. Most of the sounds have been recorded by underwater microphones.
To increase the mystery, the sounds themselves have some phantasic names: The Bloop, The Quacker, The Slow Down, Mistpouffers or simply Julia.
They sound quite intriguing but they are actually less fantastic than they appear. Almost all samples have been sped up by a factor of 16. So I reckon they would all sound the same if you were there: like a deep hum… or you simply wouldn’t be able to hear them at all. Also, most of the sounds are probably the result of geological activities after all. They just have the status of being unexplained because there is no scientific evidence yet that would link them to specific geological events.
Nevertheless, the concept is intriguing and refreshing. Most myths around unexplained phenomena often rely on the rather sophisticated sense of sight. Compared to sight, senses like hearing or smelling are much less ‘tangible’ and leave much more room for imagination. In this case, I think they create an outstanding and inspiring mystery.
