I agree with Trumpy. If the siding below the shutter is not melted and the shutter is melted, I think we can rule out heat from inside the building. So we rule out a short to ground. Do you have access to an infrared thermometer....the kind you point at the wall? You could take some readings of the different parts of the wall at different times of the day. I still think it is being caused by an external source.
