Since I use my phone in the real world where there is always ambient noise and not in a sound proof chamber, I've never noticed any hiss. I'm happily using my phone, doing videos, sharing videos, listening to music, no problems for me or my family and friends.
it totally depends on the quality of your ears, your ear lobe placement, how close you can press a phone to your face and whether or not you live in a perfectly quiet environment.
My original 7 plus had it. Only noticed it because I was looking for it. I haven't noticed it on the 7 plus I have now (I had to exchange my original 7 plus for other reasons), but I also haven't looked for it.
I dont really feel that sound on my phone. I dont think i will try figure it out. I 7+ has cracking sound issue when i twist it but i still dont mind about it.
I tried to ignore mine too, but after I recorded audio and needed to play it back full volume on my iPad Pro, the hissing was ridiculous. Completely distracting for everyone listening in two different playback environments. No such issue on my 6s plus.
That said, I'd like to know if it's been resolved as well
When I listened to my iPhone 7 and it made those noises I was almost sending it back. Then I tried my iPhone 6, it did the same thing, never noticed it.