A mechanical disk is not slient.. it will make some noise especially during spin up..
Since we have no idea if this is a loud noise or soft noise.. it is hard to say.. I so not have latest model TC.. but having used several Gen4 I can say from a few meters away I cannot hear the disk start up..
Then again the new model uses seagate drives.. !!
each time a Time Machine backup starts there is a noise which I presume is the discs starting up
You might compare what you're hearing to the sounds of this 2TB Seagate Barracuda (I gather the new TCs use the same or similar model):
Within the last day or two I think someone else was asking about their new TC making a squeaking sound that was audible as the disk spun down, rather than up (perhaps the sound heard here at around 17 seconds). They don't run in complete silence certainly.