People claiming their iPhones have problems because they hear "hissing" when recording movies.
Samsung shill YouTuber Erica something is exploiting this to damage Apple's brand.
That woman for hire is being paid by Samsung (notice on how she dismisses the low scratch resistance on the Note 7, while previously making a big deal out of it), Jerry Rig Everything does the same, its as if they are almost saying "sorry Galaxy for scratching you", but completely destroyed a Motorola phone for it.
The "hissing" while recording is 100% normal and all phones and all cameras with OPTICAL IMAGE STABILIZATION make it.
OIS works by moving the lens the other way of you hands movement, that movement will always make a soft "hissing sound" due to the coils (small motors) inside the camera assembly.
This is comparably true for the iPhone 7 series as they have large lenses with wide aperture, smaller lenses don't have the same mass and therefore won't make as much noise.
When recording in silence, the phone amplifies the gain of the microphone and the internal OIS mechanism sound is amplified.
Of course, every year they have to fabricate a couple of iPhone gates. Specially now that the main competitor have a grave problem with exploding.
However, if the camera is not being used, you should not hear any hissing obviously, if your phone makes hiss, it won't break, but if you can ear (direct, not recorded and amplified) noise at normal distance, in the silence, you should return it under warranty. That is not hiss, it's more high pitched. It sounds more like a a dentist rotary tool and less like water pouring. You can trigger not by using the camera, but for example, running a game while muted. In that case, it's called coil noise and it's very rare in mobile phones (as currents are normally low).
