Microwave runs but there are visible sparks or arcing inside the cavity, especially near the waveguide cover or metal objects.

Safety: Stop the microwave immediately and unplug it if you see sparks.

User-level steps:

• Remove any metal objects, twist ties, or foil from the cavity.
• Clean the interior thoroughly with mild detergent and water; remove all burnt-on food and grease.
• Inspect the waveguide cover for burn marks or holes; replace if damaged.

If arcing continues after cleaning and replacing the waveguide cover, a technician should inspect the cavity and magnetron antenna area for damage.