Constant Humm / Buzz but Works OK

Whirlpool Microwave Buzzing Loudly - ApplianceBlog

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Aug 12, 2011 - 10 posts - ‎2 authors
My Whirlpool MT4155SPS-2 microwave oven has recently started to buzz loudlywhen operated. The sound is getting louder and more frequent ...

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Is there any unusual noise or is it louder or quieter than normal?

A loud buzz, hum, or groan is usually a shorted high voltage rectifier diode, but a sound like gurgling into an empty coffee mug is one symptom of a failed magnetron, and yet the mag can be bad without that sound.

We have a sound clip of what a microwave should sound like when the cooling fan and high voltage section are working.

If it sounds the same as usual or a little louder, I would suspect the magnetron or high voltage diode has failed.

If it is much quieter than usual I would suspect a bad upper door switch.

The service manual is here.

Also see this file on door switches.

To allow us to help you effectively (at no charge), please post a NEW problem to FixYa, and please include your brand name and the full model number from the tag in or on the unit, your symptoms, as well as the answers to these questions:

- When you try to microwave are the inside light, internal cooling fan and turntable all working?

- Is there any unusual noise or is it louder or quieter than normal?

(A loud buzz, hum, or groan is usually a shorted high voltage rectifier diode, but a sound like gurgling into an empty coffee mug is one symptom of a failed magnetron, and yet the mag can be bad without that sound.)

We have a sound clip here of what a microwave should sound like when the cooling fan and high voltage section are working.

Note that a full Sears/Kenmore model number has 3 digits, a dot, then 8 more digits, such as ###.########

You have a bad fan inside the microwave also you need to replace 10amp fuse in order to power on.

WHEN THERE IS A BUZZING NOISE IT MEANS THAT ONE OF THE INTERNAL COMPONENT HAS FAILED .RANGING FROM A SMALL DIODE TO LARGE PARTS LIKE
THE MAGNETRON OR TRANSFORMER OR CAPACITOR. IF IT IS 10 YRS,OLD YOUR BETTER
OFF GETTING A NEW ONE .BECAUSE YOU COULD INVEST MONEY IN THIS ONE AND HAVE SOMETHING ELSE GO TWO DAYS FOR NOW.WITH A NEW ONE YOU ALSO END UP WITH THE NEW WARRANTY. HOPE I HELPED. KEN62 GOOD DAY!

the magnetron needs replacement my friend, although you can still heat up food but eventually it will soon fail.
appreciate your kind comment

Probably a bad mag, if the transformer goes bad it will draw a lot of amps and blow the fuse. If a mag shorts it just makes a more pronounced hum. Same with the rectifier. If you Ohm out the rectifier it should show open both ways as it is a really high resistance and the only way it would make a louder hum is if it shouts. so If it looks open it is probably OK, and probably bad mag. .

Possibly, the "fault" was the buzzing in the first place! Buzzing is usually a cabinet vibration caused by magnetic fields from the "gubbins". If the buzzing should occur again, try pushing/ pulling/ poking the cabinet while the oven is running, you may find a position that causes the buzz to stop.
Another possibility is you previously had something else placed in close proximity to the oven.
If a rattling cabinet is the problem, either try to reposition something, or just ignore it!

It sounds like your controller may be failing. Or it could be an electrical line problem. Any other electrical itmes giving you trouble? Has anyone measured the voltage level of your power line? It should be around 110-125 volts AC. If it's significantly lower or higher, you may have a bad connection in your breaker panel or in the wiring leading to the home.

By high-pitched, you mean it is not that same frequency as when it's cooking? Is the tone near or the same as the beep you hear when you press a key? Please post a little more information so we can help better.