Since the time of WW11 it has been known that people can hear RADAR and other types of microwave transmission.
In 1962 Allan H Frey carried out a series of experiments which proved that microwaves can produce the illusion of sound even in those who are deaf.
It is not proposed here that the Hum is caused by microwaves, these papers are included to show that the human body can detect radio waves and convert this energy into an audible sound
For 2 papers by Allan H Frey click here
For a paper by Clyde E Ingalls Clyde E Ingalls
also for a paper Hearing sensations in Electric Fields
by H C Sommer and H E Von Gierke click here