I've had the experience of NEVER hearing a sound relating to 3D Touch whatsoever...
Not loud, not quiet, not nearly silent... nothing. Nada. Never ever.
I'm assuming that is every one else's experience as well & why you can't get replies.
I don't know what you're referring to... I mean maybe I'm having a hard time differentiating the vibration from the "sound" but I don't really hear anything noticeable.