I have been trying to elimate a hum in my sound from the mixer,preamp or digita lrecorder. I have tried everything, cables, eliminating different items etc etc. I just noticed that if I touch the outside case of the mixer or the digital recorder, the hums goes away. At this point i tried with and without the power strip, different plugs in different places, separating , shutting off other stuff in the room. Nothing works other then touching the case of the mixer or the digital recorder. what should i do next?