Ok, tried it all now. All is when not touching strings
1: Through board: Noise and hum
2: Straight into GCX (skip board): Noise and hum
3: Straight into G-Force (skip board and GCX): Noise
4: Straight into computer soundcard (all running on the same power outlet): Noise
The noise level is the same so I guess that's the "normal" noise level frmo the guitars when not touching the string.
When touching the strings the hum is still present in scenario 1 and 2, but no hum at all when skipping the gcx. This is with the power supply outside of my rack. If I move the power supply back into my rack (tried various places) the hum level is increased many times.
If I listen to the power supply (outside the rack), I notice it makes a constant humming (sound higher in frequency than the hum I get in my speakers - but that could just be my ears playing tricks on me
So, do I have a faulty power supply?