New Microwave as old one's paint is peeling.
I plan to get one with inverter technology as I like those :-)
From http://en.wikipedia.org/wiki/Microwave_oven#Design
[...] Newer models have inverter power supplies which use pulse width modulation to provide effectively-continuous heating at reduced power so that foods are heated more evenly at a given power level and can be heated more quickly without being damaged by uneven heating. [...]
This is prompted by paint peeling after an unseen boilover, followed by some cooking:
From:
http://www.fixya.com/support/t7892125-paint_coming_off
We have the same problem - it started when our microwave was less than 2 years old. We had a repairman come out and suggested we use appliance spray paint. I tried that, but a year later the paint is falling off again in about 1/4 of the interior. The GE website says not to use your microwave if this happens. I just sent an email to GE complaining about it, and they offered to give me a "significant discount" on a new one. I'm not happy about it but will likely take them up on the offer, since I don't want the paint falling in our food and it's unsafe. I think this is a legitimate defect and they should be giving us new ones for free. This should not happen within 2 years of purchase!
More info than you can shake a stick at:
Notes on the Troubleshooting and Repair of Microwave Ovens: