I'm a bit late to the "iphone6s is buzzing" party, but anyways. . .
Just bumped into this iPhone 6S/S+ noise leak phenomena and decided to measure my own iphone 6s+ headphone-out for noise leak.
So i connected my iPhone 6S+ to RME Fireface 800 and recorded while using app switcher, control center and scrolling playlists etc...
And then i did the same with iPad Air2 and iPod touch 5th gen. for control.
All three devices showed about -101dB when idle but iPhone 6S+ was only device that started to leak noise when interacted with.
the "buzzing" noise of iphone 6s+ measured -96dB at it's loudest.
That -96dB isn't that huge of a deal, BUT then again. . .
CX-310 is the only headphone of mine that i've heard buzzing with iphone6s+, though it's pretty quiet buzzing, so quiet in fact that i doubt i would have noticed it without seeing certain youtube video. I might have forgot ever owning a pair of cx-310 before i saw that fine YouTube video by Lachlan, and started switching different cans and buds into iphone.
I played that -96dB noise recording in WaveLab at regular listening gain using cx-310 and couldn't hear it ....so i guess cx-310 draws more noise out of iphone6s+ than RME fireface 800 does.
It would be nice if some one could measure iphone6s/6s+ and prove that there are devices that are not affected by this noise bleed issue.
(would be surprised to see that)
Curious thing this, really a non issue for me(i don't own BAs), but interesting.