Sparking inside a microwave — visible arcing with a crackling or popping sound — requires stopping use immediately. Continued operation with sparking can damage the magnetron, burn the interior cavity, and in rare cases start a fire.
The most common cause is a damaged or soiled waveguide cover — the flat panel covering the opening on the microwave's interior side wall. Food splatter that burns onto this cover creates a carbon deposit that arcs under microwave energy. If the cover is only soiled, cleaning it thoroughly may resolve the sparking. If the cover itself is cracked or burned through, it needs replacement.
If sparking continues after the waveguide cover is clean and intact, the issue may be a failing magnetron with internal arcing, or metal particles embedded in the oven cavity from a previous sparking event. Our technician inspects the full interior and magnetron before recommending a repair path.