I am new to Moto X phone (previously had Samsung Galaxy SII - i9100).
I have Kitkat 4.4.2 on board and recently tried to listen to some music on my new phone (totally new purchased in store). Unfortunately I was not enjoying that much due to hissing sound (constant noise along with music) while listening on headphones.
I have tried a couple of headphones and it did not bring any improvement.
I was bouncing between different forums and google and found in LG G2 forum that it is a Google KitKat bug. There is a 'Xposed' module 'G2 Tewakbox' that has a fix for this. However this for G2 not all phones (I believe?).
So the question is about whether you all have the same problem? It can be easily notices when you listen on very low volume. The noise disappears around 2-3 sec after you stop music.