What could be the reason for the Microwave door to have burning spots and smell after use?
For some reason I read past &quot;9 year old microwave&quot;... well here you go:

Bad magnetron

Or this: (Personally, I'd be a little less lax on saying, eh... it's fine)

Sparking and scorch marks in microwave. What's going on here?
It's possible that either the glass or the [frozen food] allowed charge to build up to the point of arcing. It's also possible that there is something wrong with the microwave. Try putting a cup of water in the microwave and running it for about 30 seconds. If there is no arcing then the microwave itself is probably fine. If you continue to have arcing then replace the microwave.

-engineer_comp_geek, straightdope.com

Microwaves don't like ice. -thenakedscientists.com