I have a room with (4) six foot electric baseboard heaters that I have never used. Today I looked at the thermostat and found that it had two low voltage wires like a normal thermostat. I turned the heat on and heat was coming out of the heaters but I heard a humming sound coming from the 30 amp breaker in the next room. I shut it down and turned off the breaker Any ideas of what is causing this humming sound?