Spark/flame in microwave

[Starinthesky12]

Was defrosting some bacon on microwave and suddenly saw a spark/flame?!
Turned it straight off and have since used it for other food (not bacon) and seems ok.
Any thoughts on why this happened or if I should ditch this microwave?!

It might have been the bacon fat ? It might be on its way out though.

I wondered if or was the fat too - was streaky bacon. The microwave is only a year old!

Ah right, more than likely the fat and defrost moisture.

I think I might know the answer!
Can you locate the small (credit card-sized) silver square on the inside wall of the microwave? Sometimes, they get specks of food on them and small holes burn through, which eventually means you may see some sparking inside whilst in use.
They are very easily removed and replaced.

Link below for the ones I purchased.
mica sheet