Attempts at searching the forum database for threads that describe an issue with this particular unit didn't really turn up but one similar case. The problem did not occur over a period of time but started suddenly when my wife set the unit for timed heating and pushed the start button to heat water. The normal fan noise and faint hum were drowned out by a loud vibrating humming noise so my wife immediatelyturned it off and we haven't attempted to use it again since except when she recreated the event to show me what it was doing. The similar case I read about suggested replacing "the mag tube(?) and diode but that the capacitor is fine". Is the mag tube the same thing as the magnetron? My understanding is that Whirlpool made this unit and that overall, it was a good unit with few problems once the recall repair was made. Thanks in advance!