[jconrad]

Microwave about a month ago when first used in the morning has a loud
crack and a flash above the clock display. The unit works fine, there is no
smell of burnt parts. I took the control panel apart to look at it and it appears fine. any ideas? I will replace what is causing the issue, but not sure what should be replaced?

[MicrowaveDisplaycom]

Quite often this is due to grease or food particles stuck to the inside of the oven or stuck on or behind the waveguide cover.

The waveguide cover a larger stirrer cover type made of thicker plastic in the ceiling of the oven.

It can be fragile, and the metal edges of the oven behind it can be sharp, so be careful!

The cover and the metal behind it should be cleaned with a mild, non-ammonia cleaner.

If the cavity metal of the oven is chipped or charred, it will have to be sanded smooth and clean and dried thoroughly.

Then you can apply some high-temperature appliance paint, available from places like Wal-Mart, Lowe's or Builder's Square.

If your waveguide cover is burned, it will need to be replaced. It provides important protection for the magnetron.

You can usually find helpful exploded view diagrams and order parts by entering your full model number here: Appliance Parts Pros.com Discount Appliance Parts – Appliance Repair Parts