logitech z-5500. i dont know if its them or not, but after spending $950 on speakers they better not hiss. it best be that intigrated card
Logitech Z-5500 don't hiss. It's very quiet you will never know if its on if the PC does not have any audio signal coming out.
But I have experience of it humming if I have of my cheap HDD dock on. So if you have other peripherals that you use during the time when you hear the hissing, try to turn them off one by one to see if anyone could be causing the hissing.