GE Microwave Profile Spacemaker Runs on its own

Your microwave turning on by itself is a "self preservation feature" of the GE Profile Advantium and maybe some other models. Read the manual, When your over the range oven gets warm enough, for whatever reason the venting fan comes on until a satisfactory oven temperature is reached. You are not permitted to shut the vent fan off. Also it seems a temperature near room temp must be achieved before it shuts the fan motor off, it is very annoying. We had to return our Advantium because of fan noise. I configured the ovens vent fan to the recirculate direction because we do not have a vent duct that exits the house over our range. When the vent fan acting as the ovens cooling fan automatically turned on we would have to leave the house to hear each other talk. Too bad we really liked the oven other than that major problem. G-Man