Audio Systems: 60hz hum, mixer board, ground loop

Question
we recently installed in our church hall a spotlight controlled by X10 system (120KHz signal caried on our power supply to our speakers), Initially this caused no problem. Now after about 10 hours of spotlight operation it has brought on a 60hz hum to the speakers. When spot is signaled off the hum clears. Best regards

Answer
strange that it would start after working fine for a while.  If the 2 systems (unit that signals the light and the sound system unit) are both in the same room I would make sure they are pluged into the same outlet to avoid ground loops.  if this is not possible or doesnt help I would start unhooking components of the sound system until the hum goes away.  most churches have a mixer board and amplifiers, microphone preamps, etc. theres probably 1 piece that is having a ground loop problem and as soon as you disconnect it the hum will go out.  once you find that connection place a ground loop isolator (available at radioshack) between those pieces and the problem should be solved.
Let me know how it goes
Good luck!