rumble noise in background - usb

[adza]

Hey,
JD-Xi plugged in via usb to pc, sound out via mono jack. With usb plugged into pc there is a rumble noise in back ground. Un plug the usb lead the sound go's. I can minimise it by dropping gain but it's still there.
Any ideas?
Thanks

[Jovasoky]

Plug the USB cable has some advantages and disadvantages, what can you guide me or not.