Mystery Case Files · Record 26The Bristol Hum: Why a Low Sound Can Exist for One Listener and Not AnotherThe most difficult sound to investigate is one that a recorder may miss and a neighbor may not hear. I treated the Bristol Hum as a chain linking source, building, body, and attention.SettingBristol and surrounding areas in southwest EnglandPeriodPublic attention from the late 1970s onwardCor..