Try removing the TV from the equation , no connections to anything . Let any capacitors discharge .
If that does not do it , check to see if you have two outputs from a source connected to the pre .
I had a problem like yours when I had two output connections from my cable box going to my pre/pro . One analog for the CD quality music channels and one toslink for the surround sound 5.1 broadcasts . Disconnect one of the two and the hum stopped !
Good luck.
If that does not do it , check to see if you have two outputs from a source connected to the pre .
I had a problem like yours when I had two output connections from my cable box going to my pre/pro . One analog for the CD quality music channels and one toslink for the surround sound 5.1 broadcasts . Disconnect one of the two and the hum stopped !
Good luck.