I had this happen once and I couldnt get rid of it. Come to find out it was contaminated power from a neighboring apartment. Try plugging it in elsewhere and see if the problem continues. There are also several other threads on this problem. A search may get you the answer you need.
Help Preamp Hum
I am an owner of a Golden Theater GTX 1 preamp/processor. I have owned this unit for approximately a year and have really enjoyed it. Recently, I noticed an annoying buzz/hum emitting directly from the unit. I can hear the buzz/hum from a few feet away. It isn't noticable when I am playing music or watching a movie and hasn't had a negative effect on the preamps performance; however, it is annoying the shit out of me (excuse my language). I diconnected all components from the preamp, took it out of my rack, and brought it to another room in my house to see if I could duplicate the hum/buzz. After plugging the unit in another outlet, I still noticed this annoying sound. Unfortunately for me, Solo electronice, the manufacturer, went belly up half a year ago and the warranty is useless. The noise appears to be mechanical in nature and may be the transformer. I am asking for your assistance. What are your thoughts and does anyone know of a reputable repair shop in Orlando, FL or one that would allow me to ship the amp to them in the mail? Thanks in advance for your assistance.