Some computers leak A LOT of noise via USB. I have a desktop that makes even my Mackie Onyx get noisy.
Is your a desktop or a laptop?
Did you try changing the USB port?
In case of laptops, try with or without the AC charger ?
Last, but not least, ever tried a USB hub?
Sorry for the many questions. We surely have filters to isolate the USB, but filters have a limited performance.
If we were to have a device with the USB connection "totally isolated to the point that it would be invulnerable to external noise" the costs would be prohibitive.
And in this case, it is easier to work on the device that is actually sending the noise (the computer/laptop, in your case)