Thermostat concern

I recently wired a new Ranco ETC 111000 for controlling temperature on a new chest freezer. All my wiring looks correct and is seated properly. When I plugged it in on Saturday to adjust the settings, there were no issues. Yesterday I noticed that the unit was emitting a slight buzzing sound. Functionally it was still working fine but the noise concerned me. I unplugged it and opened it up to double check my connections. Again, everything looked correct, however I did notice it was slightly warm in the upper left corner by the two nodes. I have left it unplugged while I am at work today. Any advice would be appreciated.