Does it hiss at a different pitch if you're doing more graphics- or CPU-intensive applications? If so, you're hearing coil whine. If you're on a desktop, the best fix is to either use the rear audio ports or to run the audio cable connecting the front ports as far away from the motherboard as possible. I had the same exact issue, and running the cable behind the motherboard backplate fixed it.
The AUX cord is plugged into the back of the motherboard and it still is making the hissing noise, And no it doesnt make different pitches it just makes the same hissing noise at one pitch, And when i turn the volume up the hissing noise just gets louder
Hm... sound problems can have a lot of different causes. Since it is a constant pitch and corresponds to the volume, it's definitely a sound card issue and not a grounding or interference issue. In that case, yes, getting a new sound card would probably help. If you don't want to spend $50 on a card that might not fix the problem, SoundBlaster Live cards are $5 a piece and very easy to find.
It turns out that my computer is probably possessed because i have a condenser microphone via AUX and when i'm not in a Skype call it hisses but when i join one it stops completely, I just dont understand how this works
Oh, I know how to fix that. Right click on the Sound icon in the taskbar and go to Recording Devices. Disable them one by one until you find the offending port. Then re-enable the good ports and plug your mic into a different jack.
What i did was plug my condenser microphone in and turned off the playback and turned down the +db enhancer and it seem to have worked and now it has absolutely no noise unless i turn it up to a high level in that case it makes a semi low noise.