Purely academic, but:
based on press data: - 3 dB noise, which means - 3 dB SPL.
In an audio system a 3 dB SPL change would require about 6 dB accoustic power change (x4) and would give about 50% volume change (subjective).
As we are not talking about music (20 Hz - 20 kHz spectrum) but about noise of limited spectrum and our hearing subjective reaction will depend on that noise spectrum, time duration of peaks, etc... the final answer is I don't know.
Probably around 50% volume reduction (but see remark above).
Arrakis