I have a 2014 3010DS and when it is quiet I hear a “clunk” sound around the step. Sounds maybe like a solenoid. Unit is parked and jacks are down. Only happens now and then and only 1 clunk at a time.
In my 2017 2861, I hear the solenoid in the BCC operating to charge the engine battery. The BCC (Battery Control Center) is located on the side of the lower step. The BCC decides when to close the relay depending on the voltage of the engine battery and the charge voltage available from the converter when on shore power.
Linear Mode
