I just got my wolfson card today and in principle I'm quite happy with it. Getting it to work (with a custom Volumio 1.5 image from the forums) was largely uneventful. The sound (lineout connected to my stereo) is fantastic. However, as soon as I disconnect the lcd screen the audio card produces a very clearly audible low hum through lineout. It disappears as soon as the Pi is connected via HDMI to a (powered) screen. If I pull the screen's power plug or the HDMI cable it disappears again.
Since I plan to run the Pi as a headless audio player this is really a deal-breaker should there be no solution. Any help, ideas or suggestions would be greatly appreciated.