Machine Hum / Auditory OM

The Machine Hum — also reported as the Auditory OM, the Cosmic Hum, the DMT sound, or (in Terence McKenna's phrase) the audible pop — is a specific auditory phenomenon reported widely across high-dose psychedelic experience: a persistent, low, rich sound that appears to arrive not through the ears but from within or around the head, often described as machinery, a giant engine, an organ tone, or the intoned syllable OM held indefinitely.

The onset is typically diagnostic. On smoked DMT it commonly precedes visual breakthrough by a few seconds, arriving as a rising crackle or hum that experiencers learn to recognise as the sign that the full effects are imminent. On psilocybin and LSD it more often arrives at plateau, sometimes for the entire duration of peak effects. On 5-MeO-DMT it commonly fills the entire experiential field, occasionally so intensely that experiencers report being the hum rather than hearing it. Rick Strassman's DMT research participants reported the sound so consistently that he devoted specific attention to it in DMT: The Spirit Molecule.

The overlap with the sound OM (Auṃ, ॐ) — the primordial syllable of Vedic and Hindu tradition, considered to be the fundamental vibration from which the cosmos manifests — has been noted repeatedly by experiencers whose reading led them to expect it, and independently by experiencers who had never heard of the concept. Buddhist tradition treats OM as the first of the three seed syllables (Om Ah Hum) and as the sound of primordial awareness. Christian mystical accounts of the Music of the Spheres — the celestial harmonies said by Pythagoras and Boethius to sound continuously behind ordinary experience — describe closely related phenomenology. Contemporary neurophysiology has proposed several mechanisms (auditory-cortex disinhibition, tinnitus-like phenomena, gamma-wave synchronisation) without producing consensus explanation.

What experiencers most commonly report about the Machine Hum is its ontological weight: not merely a sensation but the felt-sense of hearing something that was always sounding, that ordinary consciousness normally filters out, and that is somehow generative — the sound behind or beneath the world becoming momentarily audible.

Sources:
Wikipedia — Om
Wikipedia — Music of the spheres