The microwave makes a loud "hum or buzz" noise but will not heat up the food My microwave is running and sounds like it is working but will not heat up anything.

If your microwave is making an unusual or loud humming noise, you may have a problem with the magnetron. This component is part of the high voltage circuit and provides the microwaves that generate the heat. If the magnetron is defective, it may cause a loud humming or buzzing noise

If your microwave is making an unusual or loud humming noise, you may have a problem with the magnetron. This component is part of the high voltage circuit and provides the microwaves that generate the heat. If the magnetron is defective, it may cause a loud humming or buzzing noise.
https://www.fix.com/repair/appliance/microwave/unusual-noise/

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Aug 12, 2011 - 10 posts - ‎2 authors
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A loud humming or buzzing noise would indicate a short on the magnetron circuit, the part that heats the food. These can be expensive to repair since the cost of the magnetron can be as much as a new oven. Get a few estimates before deciding whether to repair or replace.

Sounds like the magnetron circuit has failed. It is the part that generates the microwaves that heat the food. It often shorts out, and makes a loud humming or buzzing noise when it fails. It's not usually cost effect to replace since the part alone can cost as much as a new oven.

Well, if there is not heating the food and making a loud buzzing or humming sound when it is on, then the magnetron has failed. It typically shorts out and fails. The magnetron for this cost $140 plus the cost of the service call, you're better off buying a new oven. Hope this helps.

When the oven is running, does it make a loud buzzing or humming sound? If it does, then the problem is the magnetron, the part that generates the microwaves that heat the food. It not worth fixing since a new magnetron will cost almost as much as a new microwave. Ask your landlord that you need a new microwave oven. Sorry.

The loud buzzing you hear is the sound of the magnatron tube.That is what emits the microwave radiation and buzzing should be normal. The mag tube may be nearing its end at witch time you will hear no buzzing and hence no heating of foods. Replacement can be costly depending on the model so most people just opt for a new one. Hope this helps

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

Q - The microwave display counts down and the inside light is on,  but nothing is heating and the fan is not running.
A - This most commonly is a bad door switch, other possible problems are a faulty relay or solder joint on the power module, but a bad door switch is most common.
 Q - My microwave is running and sounds like it is working but will not heat up anything.
A - Many thing can do this but, common things are....loose high voltage wire.....poor solder joint on board.....magnetron.....power relay.....
Q - The microwave makes a loud "hum or buzz" noise but will not heat up the food?
A - 9 times out of 10 this is usually this is a bad magnetron, the other time is sometimes a bad high voltage diode. See components section.