OCZ PSU making a hissing sound

It's either making that sound because some component is stressed or overheating, or the PSU fan is making that noise because it's crapping out. You could try blowing it out with compressed air, just don't inhale any of the dust that comes out of course. Looking at your configuration it shouldn't be stressed out so it could be dying. If it's just the Fan I wouldn't recommend replacing that if you don't know what you're doing since you can shock yourself pretty bad with those darn capacitors. If you blow it out and it still makes that noise I would turn it off and not use it again until I got a replacement power supply.