'The Hum' is an unexplained low-pitched sound heard in many locations worldwide. It was first reported in the 1960s in England. Roughly 2-10% of the population can hear it in affected locations. Its source has been difficult to track in most places; it's not known whether it is one phenomenon or different phenomena in different areas. Scientists in New Zealand claim to have caught it on tape in 2010, but there is skepticism of this recording. The record here is dated 2012.