I am an electronic engineer and have the exact same issue with my earbuds and this annoing hissing noise. As electronican I can tell that this sound should come from the amplifier that is in the earbuds. As soon as this amplifier is turned on, this hissing noise is there. It sounds like a bad calibrated amplifier.
I would accept this for a 50 dollar thing. But I will not accept this for 200 dollars. How can I get a replacement?