Background noise problem

I have a problem with background noise. My interface is set up properly (i am using an alesis multimixfx 8 usb) and when running standalone is great quality, no noise.

When connected to USB it is still perfect but the moment I load cubase I get a very high hissy noise that is driving me mental.

I am getting meter activity on all inputs on cubase mixer (not hardware) and when I mute the inputs the noise is still present so must is originiating from cubase itself and so present on all signals in and out.

Anyone got any ideas as this is a menace.