unfortunately this is probably the magnitron, this is something thats very expensive and you need a tech to replace, microwaves have very high voltage that stays in the machine even after its unplugged, do not attempt this repair, this can kill you, yopu say this is under 5 years old I would call G.E. this may be under warranty for 5 years, this is the goverment warning on these,
Consumer Product Safety Commission
Electrocution Hazard with Do-It-Yourself Repairs of Microwave Ovens
CPSC Document #5061
The U. S. Consumer Product Safety Commission (CPSC) warns against do-it-yourself repairs of microwave ovens. Each year, on average, four people die from electrocution trying to repair their microwave ovens. Microwave ovens use high voltage which makes it particularly hazardous for consumers to remove the cover and touch electrical parts. The possibility for electrical shock from a microwave oven still exists even after the oven is disconnected from the power source. Should certain internal devices fail, even unplugged ovens can cause serious injury.
The Commission strongly recommends that consumers have professionals repair microwave ovens because electrical appliances can be hazardous if consumers expose live electrical parts.
Removing the cover of your microwave oven and touching an electrical part can kill you.
Have a professional repair your microvave oven