I just uploaded a video of the buzzing/hissing sound coming from my iPhone 7 Plus. I shot this on an iPhone 6S Plus; no special microphone and no post editing involved. This is a pure albeit crappy video of the sound.
iPhone 7 Plus 128GB Black AT&T
https://youtu.be/CXh9OSQYiCY
iPhone 7 Plus 128GB Black AT&T
https://youtu.be/CXh9OSQYiCY