To answer your question I used circuit below and made sound box, using medicine jar, to increase output.In the post #38 circuit, when the lamp is working there is about 130mV rms across the piezo. Is that likely to produce an annoying background sound?
Threshold of sensitivity for me was about 10 cm (from sound box hole to ear).
I heard soft 50 Hz sound.
For younger people threshold was up to 50 cm.
They heard crisp sound.
Sound box:
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