K, I do think some of it is human perception of sound. For instance, in an episode of 'Ghost Lab' when investigating the Granbury Opera House, purportedly haunted by John Wilkes Booth, the EVP they captured, to me sounded like an adult from Peanuts, that wahwa wah wahwa sound. Hmm, they could have used the WahWah Machine to be sure....
Seriously, listen for yourself, A Whisper From the Grave
'American photographer Attila von Szalay was among the first to try recording what he believed to be voices of the dead as a way to augment his investigations in photographing ghosts. He began his attempts in 1941 using a 78 rpm record, but it wasn't until 1956, after switching to a reel-to-reel tape recorder, that he believed he was successful. Then, in 1959, Swedish painter and film producer Friedrich Jürgenson was recording bird songs. Upon playing the tape later, he heard what he interpreted to be his dead father's voice and then the spirit of his deceased wife calling his name. He went on to make several more recordings, including one that he said contained a message from his late mother.' (Wikipedia)
Looky here- The New York Times Halloween in Manhattan’s Most Expensive ZIP Codes