I still have my 16 Pro alongside my 17 Pro. My 16 Pro also has a subtle hissing sound when the rear camera is open that goes away when switching to the front. Same as my 17 Pro, you can hear it if you put your ear up to the front earpiece as well as up to the camera housing on the back. The 17p’s hiss might be ever so slightly louder or maybe just a slightly higher frequency. But it’s definitely happening on both.
As for the clicking, both make a clicking sound when opening the camera app that you can only really hear if your ear is up close. It sounds to me like it’s the hardware engaging. I’ve been unable to recreate the Face ID sound mentioned by the OP.
I’ll also add that if the camera is open (17p), and my ear is focused on the rear housing, if I shake the phone I can hear the occasional very light tick/pop - I can’t make that happen on my 16p near as often, but can make it happen (goes away when camera is closed).
I think all of this might just be the stabilization hardware doing its thing.
I’m not saying the OP doesn’t have a legit concern with their unit, but when I see similar behavior on my 16p, I think it’s as designed, and we’re just in that phase of analyzing these new devices to a level only known by us forum enthusiasts. 🙂