No. 100: Jul-Aug 1995
Vets at the Animal Health Trust in New Market, UK, had just removed a tumor from the lip of a 5-year-old Welsh pony, when they heard a strange, high-pitched hum emanating from its right ear. The hum was surprisingly loud and quite obvious to the surgical team standing a meter away. The hum's pitch was a steady 7 kilohertz.
E. Douek, an ear, nose and throat surgeon, stated that audible sound coming from ears is extremely rare. Such sounds are usually caused by muscle spasms in the inner ear or throat, or by resonance due to abnormalities in the ear's blood supply.
(Bonner, John; "Humming Horse Puzzles Vets," New Scientist, p. 5, April 29, 1995.)
Comment. This is not the first time we have heard about humming ears. In SF#31*, H. Zuccarelli stated that human ears normally emit a faint reference sound, which mixes with incoming sound to form an interference pattern inside the ear. The resulting "acoustic holograms" allow humans and some other primates to locate the source of a sound without turning their heads. The affliction called "tinnitus" is evidently not involved.
*SF#31 Science Frontiers #31. The book Science Frontiers also contains this reference. It is described here.