Graham had been a noise enforcement officer for thirty years. He was thorough, methodical, and had responded to approximately four thousand noise complaints. He was also, unbeknownst to himself, developing high-frequency hearing loss from three decades of measuring nightclubs.

One Tuesday, a resident called about a high-pitched whine coming from a neighbouring property. Graham arrived, deployed his Class 1 meter, and waited. The meter showed 28 dBA — essentially silence. But Graham could clearly hear the whine.

He moved the meter closer. Still 28 dBA. He changed the weighting to Z. Flat response across all frequencies. Nothing above the noise floor. He checked the cables. He replaced the batteries. He tried a different microphone capsule.

The tone persisted. Always at the same frequency. Always at the same level. Even — and this is when the penny dropped — when he was driving home with the windows up.

Graham's audiologist confirmed what the meter had been telling him all along: the tone was at 6.3 kHz and existed exclusively inside Graham's head. Thirty years of 'just popping into the club to take a quick measurement' without hearing protection had left him with a permanent souvenir.

The Moral: If your measurement mic can't detect a sound but you can hear it clearly — and it follows you home — please see an audiologist. And use SonaVyx's noise dose tracker to monitor your own cumulative exposure. Your ears are irreplaceable; your measurement gear is not.