I need someone who notices the 'hiss' to try something for me. If you have a pair of headphones that DO NOT have a microphone on them, plug it into your phone and let me know if you notice the hiss noise. (Headphones without a mic will have 2 black lines on the 2.5mm jack. Headsets with a mic will have 3).
I've noticed the noise is not present when I plug the phone into my car stereo, and the cable I use is a standard 2.5mm stereo cable. But, it could be that I simply can't hear it in my car, where I can with headphones. I want to test this idea with a pair of standard headphones, but I don't have a pair.