The Hum is a generic name for a persistent low-frequency sound reported by approximately 2-4% of the population in locations around the world. First documented in Bristol, England in the 1970s, similar complaints have since been reported in Taos (New Mexico), Windsor (Ontario), Auckland (New Zealand), Bondi (Sydney, Australia), Largs (Scotland), and dozens of other locations on every inhabited continent. The sound is typically described as a low, rumbling drone similar to a distant diesel engine, most audible indoors and at night. It is often accompanied by sensations of vibration or pressure.
What makes the Hum particularly challenging to investigate is its selective audibility — in any given location, only a small percentage of the population can perceive it, and acoustic monitoring equipment typically detects nothing anomalous. This has led to two broad categories of explanation: environmental sources (industrial machinery, gas pipelines, electromagnetic radiation, ocean microseisms) and physiological sources (spontaneous otoacoustic emissions, tinnitus, or heightened low-frequency sensitivity). The phenomenon remains one of the most widespread and poorly understood perceptual anomalies in the modern world.