We are getting a humming noise from a solenoid in the forward engine compartment. It seems to be getting louder and quite annoying. There are two solenoids in a box similar to one that Newmar uses for their Bird System where the humming originates, but I don't think we have a BIRD system on our older coach. It is noisey on 12v but is louder on shore power. Is this normal or does this happen if a solenoid begins to fail? The coach is new to us and we didn't notice it until recently. We installed a better converter back in January keeping it plugged in all winter and am wondering if this could have affected it as it has a de-sulfication charge at 14.2 v that runs every few weeks.
Freightliner Chassis, Cummins engine, FMCA #408511