What Is The Mysterious ‘Global Hum’ — And Is It Simply Noise Pollution?
However, Elizabeth Silber, a Canadian physicist and planetary scientist who investigated reports of a hum in Windsor, Canada, says: “There are many natural sources … such as aurorae, lightning, meteors, volcanoes, waterfalls and ocean waves. An original researcher of the microwave auditory effect, James Lin, now at the University of Illinois, believes this hypothesis is a non-starter, pointing to the fact the microwave auditory effect requires a signal that is pulsed, which would not yield a constant hum sound. According to Geoff Leventhall, a senior acoustician who specialises in low-frequency sounds, possible urban culprits do in fact include acoustic noisemakers: “Ventilation fans on large buildings, air compressors, diesel engines, either as traction sources like buses, or stationary, such as diesel-electric generators, air or water pumps.”
Source: www.theguardian.com