Bought a 7 (not plus) last Friday. Have been following this thread and also the "yellow screen" thread with some interest. Have checked the screen and it has exactly the same color temp as my rMini just a little brighter under full brightness. It definitely does not look yellowish so I guess I was lucky when it comes to the screen.
Anyway, today I finally put the back of the phone to my ear... and yes it is hissing.
Not only hissing (which varies in frequency and character) under load, it's also makes a ticking sound when idle, almost like a clock at nearly one tick per second. However, both sounds can only be heard when holding the back of the phone to my ear or maybe one or two centimeters away.
Then I got an idea... Maybe I should check my Sony Z3+ which I have had for over a year. Said and done. Guess what! It does also make this hissing sound! Just a little different in frequency and overall character. It is a little "smoother" but maybe also just a bit louder. When idle this phone makes some "squealing" sounds now and then, not directly the constantly ticking one as on the iPhone. The Sony phone also gets very warm very quickly so if you put the phone under load it is not very pleasant to hold it up against your ear for very long... To sum it up. Not sure what I should do with the iPhone. Since this hissing sound hasn't been an issue at all with the Sony phone for over a year I guess I will be fine keeping the iPhone, especially as the screen doesn't have the yellow tint at all. Actually, now it is just that irritating ticking that bothers me the most...