Why is there arcing or sparking inside my microwave, and how do I fix it?

Arcing or sparking is typically caused by using materials that should be avoided in the microwave, such as aluminum trays, metal-trimmed utensils, metal twist ties, or food cartons with metal handles. The remedy is to use only microwave-safe cookware, and to ensure food refuse or uncleaned residue is not present in the cavity. An uncleaned cavity cover located on the right side wall can also cause fire, burn, or sparking, so clean the oven regularly with a wet towel. (Pages 7, 27)