Gefen 2x2 VGA Switcher Noise

When I turn the volume to max on my mixer and move computer cursor around the desktop I am getting a scratchy sound from the monitor speakers.

Prior to using the Gefen Switcher I ran the audio directly from the computer to the mixer (Mackie 1402-VLZ)and on to the speakers, I didn't get the noise.

The cables Gefen supplies - 3.5mm stereo plugs look real cheap. They connect the computers with the switcher. The other cable which connects the switcher to the mixer is a 3.5mm stereo plug to RCA's. I've tested several high quality (3.5mm stereo plug to RCA's) cables but the noise persists.

I've got the switcher about 9 inches away from electric parts (monitors, battery backup, external scsi hard drives, etc) but some of the cables are very close to some electric devices. I'm not sure if taking further action in isolating (ie moving further away) the switcher will solve the problem other than getting higher quality cables conecting the computers and the switcher. I was looking at Canare but they run about $22 apiece for 6ft. I could also use 3.5mm stereo to xlr but that might be overkill and not solve the problem.

I'm not an audio expert but do you think the product is defective? A grounding issue? Any ideas would be appreciated.

Oh, there is a set of usb cables connecting the computers with the switcher. Could electrical interference be introduced with these?

Thanks.