Got a 0.2 second beep while walking by the Old Market. Felt like it hit directly behind my right ear.

Happens near the subway tunnel by the station too. That place amplifies weird frequencies. They travel upwards.

Had one at 1am while I was watching the pixel glitch threads. Short, metallic, like a microwave finishing but quieter?

Mine had harmonics. A big tone with tiny tones fluttering under it like wings.

I recorded one accidentally. Waveform is too clean. No ambient noise around it. Just the tone. Perfectly isolated.

You are hearing the precursor. The shapes announce themselves through sound.