Macbook pro 13 Late 2011 Hissing Headphones FIX
Hi I've recently come across this 'hissing' low noise in my headphones, which start the moment I plug my headphones in. I went through multiple threads on this and people just don't have any fix for it. I have a fix for it; that worked for me and may work for you depending on the circumstances.
Firstly, I have a Macbook Pro 13.3 late 2011 model. Never had this issue. I'm on the newest Yosemite. Nothing has changed with my macbook, expect one thing; my hardware setup. My charger cable had broke, so I had to get a new one. I bought it from a site called 'miniinthebox'. This was the change. Something so simple; a cheap quality charger, which when plugged in, made this noise that was unbearable. I'm assuming the cheap wires and materials used in this charger caused static with the power and outputted this sound.
TL;DR
If you just recently bought a new charger, or a new cable or any sort for your macbook, try and unplug it and see if the sound changes. My 3rd party charger is the cause of the hissing.
Hope this provides some fix for anyone in the same situation. Good luck
MacBook Pro (13-inch Late 2011), OS X Yosemite (10.10.2), Hissing Headphones