I have set up a very basic mini solar system at home. 1 panel, basic inverter and leisure battery. Been using the system for over a year. My invertor is now screaming as soon as I turn it on, nothing is connected to draw from it, the battery has charge. (Tried changing it to a different one also) When I turn it on, the fan is instantly coming on and makes a large draw, goes up and down for a few seconds then stabilises ok but still screams. Any suggestions greatly appreciated please