The base on one of my two Nest T4000 all of a sudden started buzz even with the thermostat removed. I removed the wires and cleaned the ends and no change. It is a two wire system that has been working for four or five years with no issues. So both are connected to the same power supply and only one makes the noise. The wires are the typical solid copper and the one that is buzzing is about 10ft from the transformer. I have read all kinds of bad info from I have to have the C wire to electronic stuff makes noise all the time. Has anyone found the root cause?