Is there a fan in there??

I heard what sounded like a muffin fan running behind the fuse/power box located on the bathroom wall. Is there a fan in there?

The converter has a cooling fan that is thermostatically controlled. When the converter is called upon to provide lots of current, it may occasionally run. There is also a fan under the tub on sone models (bathroom exhaust fan) operated by a switch.

Thanks Bob, Yeah, I know about the vent fan and switch, and I was running the AC so that certainly explains it I think. First time I ran the AC more than 30 seconds.

I may need to see about swapping the cooling fan though, it sounded like it was 1/2 dead and could quit at any moment. Speeding up and slowing down......rough bearing sound.

AC or any Alternating current appliance should not effect the fan. That is primarily used to cool the convertor when it is converting AC to DC to charge battery or run 12V appliances. If you had a low battery when you connected to shore power, that would start the fan.