So. I bought a second hand ABM EVO 300w. It hums like a bitch. I rigged a plug without the earth connected. It still hums, but when I touch the screws on the VU meter, the fan on the back or the D.I. socket, it goes quiet. I then tried it with a standard plug lead but with the earth wire inside the amp disconnected from the power lead input socket. Same thing, hums to start with but if I touch any screw or the D.I. socket the hum disappears. Any suggestions as to where to go from here to fix it? Thanks all.