adam666, Not knowing your power supply. What type. Transformer hum is Magnetostriction - the contraction of materials in a magnetic field which, among other things, leads to the hum of transformers whose metal cores contract and expand as the current in their coils changes with time.
I'm not much of an electrical guru. But hey.. worth a try. In my home, I had a hum in my Old Dolby sound system. I started to unplug everything on that circuit, Well It was a lamp. A halogen lamp on the same circuit. Average conversation measures about 60 decibels. The purring of the family cat rates about 25 decibels. Blood coursing through the human body makes a measurable sound -- about 10 decibels. At the other end of the noise scale, an average typewriter produces 70 decibels of noise; a printing press 80; a subway train 100; and a punch press 110 decibels. Above 120 decibels, sound becomes painful and can be felt as well as heard.