Annoying speaker whine/hiss

I recently bit the bullet and decided to shell out copius amounts of money upgrading my aging computer. Aside from a minor hiccup with keyboard not being recognised during the windows setup all went well. That was, of course, up until the point I decided to test out my speakers.

It would appear that there is some very odd noise being generated somewhere, and I am currently inclined to believe that this is a software issue.

The speakers work fine when connected to other audio equipment, so am confident the speakers are not at fault. I was originally using the on board realtek HD audio however I switched to my old Creative X-Fi sound card when I noticed the problem, but still it persists.

I've muted all the input sources that I can find. Uninstalled and re-installed all the drivers. Windows 7 is up to date. I cannot think of anything else that might casue this. The noise isn't your usual buzz, it seems vary in intensity ever few seconds, and frankly just sounds odd.

Does anyone have any idea what might cause this? Are there any known sound issues with Windows 7?

Motherboard: Asus P8z68-pro
OS: Windows 7 ultimate.

Why not try a new speaker?
Could you try to borrow some other speakers?

I have tried headphones which have the same problem as the speakers.

I am going to attempt to change the PCI slot the sound card uses, but I'm not too hopefull this will work as the same problem is manifest with both the discreet and onboard sound cards.