Reply to USB Signal Noise

Hi Guys,

Having some trouble with my pair of Xone:K2s.
Ever since I got them, there's been a low volume, high frequency noise emitted when connected via USB.
Here's my setup.

Macbook Pro 13"
2 x Xone:K2
1 x XoneB2.

1 Xone:K2 connected through a hub.
1 Xone:K2 connected directly to USB port.

Anyway, I haven't really cared up until now as it's hard to hear while playing, but it becomes evident during silent/low volume periods.

Note: The signal noise does change depending on how many LEDs are lit up on the device, but it is still there when there are none lit up.

I've tried different USB cables, ones with RFI chokes, different ports, direct connection etc.
As soon as the USB cable touches the socket, it starts to whine.

Is anyone else having this issue/know of anything I could do do eliminate it?

Cheers