If you live in a thin-walled apartment or share a bedroom, quietness is a feature, not a bonus.
What "quiet" means
Under 50 dB at full power is "muffled by a duvet." Under 40 dB is essentially imperceptible from the next room.
Picks
Specific recommendations rotate as new product comes in — check the vibrators collection's "feat:whisper-quiet" filter for the current shortlist.