Electrical interference in desktop system

While auditioning Focal CMS 40s speakers as part of a computer desktop setup*, a high pitched tone audible from some feet away led me to discover that the speakers are designed with virtually no electric shielding. Their tech support (email) said this was an engineering decision to get the best sound. With one pair of good quality unshielded ICs, I'm not only hearing a high pitched tone, but also mouse movements can be readily heard. And that was using better AC cords; with the ones that came with the speakers, it was even louder. Trying another good unshielded IC pair, noise returned to an ear-to-speaker level. Since I've never experienced this degree of interference before with either IC (or others) and other good desktop speakers, I'm not sure the best way to handle it. Tech support says better AC cords help, but mainly its in the positioning of everything. Anyone have experience in handling this problem with a desktop setup (in a small spare bedroom)? Thanks,

* System: Computer (Win 8x64 Pro) to Ciunas dac (John Kerry) via two USB adapters off USB card, and then ICs to the speakers.
Any thoughts? I've just received a pair of Teresonic silver ICs and it's like listening to the inside of the computer with soundstaging.
try putting the PC on a filtered power strip and look for twisted pair interconnects as a defense against RFI.
To pick this up again, I've tried both the Panamax M5300-EX line conditioner and Mapleshade power strip (Mk II Plus) with the same result. Starting with the Focal speakers and Dell monitor plugged into the conditioner/strip, if I plug the computer into the old style console the electrical noise is inaudible until I hold my ears tight to the speakers, and even then it's light. But if I plug the computer directly into the conditioning unit or strip, a high pitched hash/buzz becomes audible from the listening position (3 feet) and at times is even like soft music audible between the speakers. Of course, using the the strip gives a bit more clean and delicate sound than thru the console (MAC HC or Venom 3 for speakers and computer).

So I'm wondering, is there a way to solve this short of a regenerator or a specially built PC. Thanks,
Curious, are you able to try a laptop instead? Wondering if this issue is noisy PC power supply... you can run a laptop on battery.
Hum-X quieted it down, now almost inaudible ear to speaker.