This thread was previously titled "delete".. so I though of posting something instead of just leaving it blank.
 
My monitor speakers pick up noticeable but soft noise (sort of whooshing sound) when I move the mouse or scroll the webpage. It's been going on for a while.
 
I've decided to give the Behringer HD400 a try.. and I'm happy to say that it works well. No noise, hum or hiss when I turn up the Quad Capture vol to max (when there is no audio running). I'm really happy with the result.
 

..bump (for the update)

Sounds like System Sounds are still turned on.  I have Windows System Sounds disabled (none). 
 
I have an Octa Capture and do not get any "swooshing" sounds like you are (were) getting.  I have my studio monitors connected directly to the Octa Capture.

Fireberd, thanks for the suggestion.
 
Now I had my Windows Sound set to 'no sound', as well as disabling the Windows sound device. Removing the HD400 and the whooshing sound is back (have to place your ear next to the monitor to hear it). Placing the HD400 back, again removes the noise. I suspect it may be due to me staying quite near to the power line. It's about 400 to 500 km meter away.

That HD400 is for a "ground loop hum" problem.  You must have a ground loop problem rather than what you are describing.
 It is copied after the EB-Tech hum eliminator.

That might just be the case. All my power supply came from a single wall outlet, through a power regulator, but that didn't help. My guitar sounds noisy at certain times, otherwise it's clean.
 
I actually bough the EB-Tech hum eliminator (XLR) at the same time too, but have not tested it yet. Hoping to get a clean guitar sound from the EB-Tech.. otherwise a call to the electrician may be in order.

I also have a Quad Capture and used to get this problem. For me the problem occured when running my old Dell laptop from the mains supply - laptops (particularly Dell) are notorious for this problem. Of course I could have run the laptop on batteries, but this is far from an ideal solution.
 
I solved it on my rig by flipping the ground lift switch on the back of the Quad Capture - this eliminates the problem for me. However, I've also changed my laptop too, and don't actually need to have the switch engaged - but it certainly helped when I had the dell.

Gary,
 
It's an odd problem for me, I've tried flipping the ground lift switch of the Quad Capture, but somehow, the noise level seems higher after doing so.
 
I've also managed to clean up the grounding issue I can think off. Once there is a small leak, I felt small current running through the metal parts of the Quad Capture, my guitar string, etc.. it was traced to a bad power plug multi socket. After changing that, the leak is gone, but the noise still persist.

Not sure if this is related, but I used to "hear" mouse movment on a system I had. It wasn't a woosh, but a sort of putt, putt, putt noise as the mouse moved around. You only noticed it with headphones on. I wrote it off as some sort of RF interferance genorated by the mouse sending info to the MOBO.
The mouse was hardwired USB.