Microwave over Oven combo. Read that running a self cleaning might clean grease off the cooling fan. Fan did run in self cleaning mode. More research found fan has two speeds. Removed oven door, panels and pulled both units part way out. Disconnected microwave connectors and lifted it off the oven. Removed fan cover. Fan didn't feel like it was turning free. Used an AC test cable to test the fan. Wouldn't turn on one connection and slowly on the other. Fan bad. Removed back panel to access all screws, disconnected the fan rotation sensor. Ordered new fan, received it in just two days FedEx! Installed and all ran great. (Only had four screws left over) Should have taken pictures as I was talking it apart.