here's a stupid question....... when i park my fifth wheel in my driveway between trips i usually leave it plugged into my house. i have noticed that on several occasions a whirring type noise coming from the fuse panel/invertor area. it is also quite warm to the touch. is this normal??? i know that the invertor will keep the battery charged up fully, but should be idle once the battery is fully charged. while the trailer sits there is nothing on, except the fridge, but its ac power.