phays Doug, I'm afraid my documentation does not show any fuse or wire identification with the information you have.
Since the circuit is active with the key off I would assume the circuit is part of your domestic components. You could perhaps verify this by turning off your house battery with the "salesman" switch. If the noise does not begin again with the fuse installed then you have at least identified a group of components that are controlled by that fuse.
If the circuit is on the domestic system then I'm not sure there will be any comparison with our coaches since those components are installed when the house is added to the chassis. If it were on the chassis side then there may be some comparison.
My immediate thought on the squeal is that it may be an electric motor with a bad bearing.
Sorry that I can't come up with anything specific.
Pete, thanks for the response. I verified that the circuit in question is indeed active with the key off and the salesman's switch off. Like with headlights, door step, horn and various other circuits, and unlike cabin 12v interior lighting, vent fans, and the generator starting circuit (Circuits that you are calling the domestic system). So I didn't find the source or the problem components, but thanks for looking at your schematics.
2003 National Tradewinds LTC on CC Dynomax Chassis (one rare RV)