Since the early 1990s, some residents around Taos, New Mexico, have reported hearing a persistent low frequency sound that others cannot detect. Descriptions vary from a distant diesel engine to a vibration that becomes especially noticeable inside quiet buildings.

This episode examines the investigations into the Taos Hum, the difficulty researchers faced in identifying a common acoustic source, and the scientific explanations proposed for experiences known collectively as the Hum. The reports are genuine experiences, but whether every listener is hearing the same phenomenon remains uncertain.

If no single external sound explains the Hum, what exactly are some people hearing?