That 6" fan definitely isn't silent but pulls enough airflow to allow for "max" 110V hashing (15.5Th/s @ 1350W). It's louder than a typical bathroom exhaust fan but not as loud as a kitchen range hood. But similar in tone (i.e. not the annoying high-pitched whine of the stock fans).
I don't mind it running in the same room as me, but it's too loud to do a Zoom call near it.
https://twitter.com/KeithMukai/status/1605644949013368834
The 4" fan IS silent enough and could happily run right under someone's work desk.
https://twitter.com/KeithMukai/status/1603944134385045505