Does anybody else have this issue?
I had a very extensive and helpful reply from NuForce but it pointed towards maybe a IRQ issue or perhaps not enough RAM etc.
My MBP has 8GB of RAM and I had just finished rebuilding my Mac onto a brand new hard drive. I was only running iTunes when I reconnected the u-DAC.
On a keyboard press, the output distorts and "warbles" badly for about 6 seconds then goes back to normal.
Currently, the only solution is to reboot.
If nobody else in the World has this issue, I guess I have a fault DAC but it's well out of warranty now.