The wife called GE over the weekend and the repair guy said it was the wave
guide at fault. He said GE would be in contact with me in the next 48
hours to schedule to replace the unit, as the defect was under warranty.

Seemed odd to me, as the unit is 4 years old.

I looked up some info on these wave guides...tried cleaning the cover of
the wave guide; the problem (buzzing) is still there.