I had a hum caused by me Eastern Electric MiniMax DAC Plus when I added it to my system. I used an Ebtech Hum-X with it and the hum went way. I got the Ebtech Hum-X from Guitar Center on sale during the holidays. It is a safe cheater plug that can handle up to 6 amps of current.
Like others have stated start at the preamp and sources first.
Like others have stated start at the preamp and sources first.