[Electronic Ignoramus]

Though all else works, my microwave doesn't heat. When starting, it initially makes a crackling sound which goes away and changes to a loud hum or buzzing sound. Often it trips the breaker as well. In any case, a pungent odor comes from the vent....a smell of overheated electrical components.

[appman]

buy a new one ... bad magnetron tube or high voltage transformer. it will cost as much to repair as it to buy a new one.

[microwavedisplayDOTcom]

It sounds as though your stirrer might be arcing but I'd say your magnetron is bad. It may possibly be the high-voltage transformer, but from what I've seen of GEs, it's probably the magnetron.

If you or a friend want to check it out, you can usually find helpful exploded view diagrams and order parts by entering your full model number here: Appliance Parts From PartSelect | Repair Parts For Major Appliances.
Otherwise, I'd contact GE for an authorized local servicer or a replacement model recommendation.

It can run as much as $250 for a tech to come out and replace a (GE) magnetron. Food for thought for what its worth.