Please help I have a strange grounding problem

I recently bought a FIM 880 outlet and installed it myself. I plugged in my amp and cdp but I'm getting a fairly loud "humming" when I play my tuner only. I don't have dedicated outlets( I'm in the process of making this my next project)so I have my tuner plugged into a Monster Cable 2000 outlet which is in another outlet on the same wall.Both outlets are on the same line as when I shut off the breaker there is no power on this wall. The strange thing is when I unplug the cdp, the hum goes away completely.It only comes back when I plug the cdp back into the same outlet as my amp. Another weird thing is when the hum is there and I get closer to my amp, the hum increases in volume as if my body is acting as an antenna. I'm not a technical guy,but it appears to me that there is some kind of a loop and by unplugging the cdp the loop is taken out. I would surely like some advice on this new and strange situation. Thanks for your help and advice.