Manifestations of a low-frequency sound of unknown origin perceived worldwide, also known as "the Hum" or the "Taos Hum".

INTRODUCTION: "The Hum" and "Taos Hum" are the common terms used for an annoying low-frequency sound of unknown and seemingly mysterious external causes. The Hum is a phenomenon occurring worldwide that affects approximately 2% of the population, called hearers or hummers.

OBJECTIVE: This study investigates the different manifestations of the Hum based on questionnaires tailor-made for hearers, with the aim to demystify this phenomenon.

MATERIALS AND METHODS: Questionnaires completed by 162 hearers were evaluated, with a focus on three often-reported features: whether their Hum forms beats with external sounds, whether head rotations remove their Hum, and if air travel produces a time lag until the Hum reappears.

RESULTS AND CONCLUSIONS: The presence of at least one of the three features is typical of the Hum for 73% hearers. The three features are statistically significant dependent on each other. Hum-oscillations are typically influenced by head rotation and by sounds and are most likely located in the semicircular canals and the cochlea. Therefore, for the majority of hearers, the Hum may represent a rare form of tinnitus that has nothing to do with external sounds. The remaining group doesn't experience any feature of a typical hearer.