Is it common for these to make a humming noise? I thought they are normally quiet since there are no moving parts. The noise cycles on/off maybe 5 min intervals. I had it set in "auto" mode since we've turned it on a few weeks ago, plugged into shore power. We've been using LP for the furnace and water heater. I assume the fridge runs on AC when in auto mode even though the LP tank is open?? I have since switched mode to AC. Will see if that stops the noise when we go back to the campsite.

Kevin