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.