Microwaves are hardworking kitchen appliances, and it’s understandable that they sometimes have problems. However, what does it mean if your microwave makes noises when it’s off?

Your microwave making a noise when off is not something to worry about if it’s still heating food correctly and working normally. Microwaves sometimes make noises when they’re off because of hot parts, magnetron issues, a faulty fan, diode problems, or power supply issues.

I’ll explain in more detail below the reasons a microwave might make noise when it’s off. I’ll also discuss whether there’s anything you can do about this issue.

Why Does Your Microwave Make Noises When It’s Off?

It’s normal for a microwave to make noises as it warms up food. So, what does it mean if your microwave makes noises when it’s off?

Your microwave makes noises when it’s off because of hot parts, the transformer, magnetron issues, a faulty fan, power supply problems, or diode problems. These problems are more common in older microwaves or ones that are used extensively.

I’ll discuss these common microwave issues in-depth below:

Hot Parts Might Trigger Fan Activation

A microwave’s primary function is to heat and cook food, and it’s only natural that its parts will get hot during the process.

If you’ve been microwaving something for an extended period, your microwave can get incredibly hot, but thankfully it has a thermostat that detects when the parts are getting too hot. The fan will start running to help the hot parts cool down when this happens.

Your microwave’s fan can continue running even after you’ve switched it off, and the noise you hear could be the fan rotating. The fan should stop once the parts are cool. However, if the noise doesn’t stop once the parts have had time to cool, you might have one of the following issues on your hands.

Magnetron Issues Are Common in Older Microwaves

Older microwaves can develop issues with the magnetron. This causes it to make noises, regardless of whether the microwave is on or off.

Your microwave’s magnetron is its most essential part because it’s responsible for releasing high-speed electrons in a magnetic field. The high-speed electrons generate microwaves, which disturb your food’s water molecules, create heat, and cook the food.

When your microwave is on, it’s normal to hear the magnetron making the occasional clicking sound. However, if your microwave is off and the magnetron makes noises, it might be faulty.

If you hear snapping, humming, or buzzing sounds when your microwave is off, it could be the magnetron.

Faulty Fans Lead to Abnormal Sounds

If you regularly cook food for extended periods in your microwave, the microwave’s parts can overheat, causing the fan to work hard even when the microwave is off.

Your microwave fan can wear down over time and struggle to work correctly, which is typically a problem with old microwaves. Dislodged food can also get stuck in the fan, causing it to work inefficiently and make a strange sound.  

Diode Problems Create Crackling Sounds

Older and heavy-use microwaves can sometimes develop diode problems.

A microwave’s diode is responsible for powering the magnetron and converts alternating current to direct current. When your microwave is on, the diode makes a humming noise, but a faulty diode might make crackling sounds when the microwave is off and cooling down.

Transformers in Microwaves Often Make Humming Noises

All microwaves have transformers that convert the electricity from your power supply into higher voltage energy to heat your food.

When your microwave is plugged in but turned off, the transformer powers the digital clock. Because of this, you might hear it making a low humming sound even after you are done using your microwave. This is entirely normal and nothing to worry about.

Power Supply Problems Contribute to Abnormal Sounds

If your microwave is off, still plugged in, and makes strange noises, it could be due to a power supply problem. Even when it’s off, your microwave still needs a small amount of electricity to power the clock and keep it in standby mode.

A frayed power cord, faulty plug, or a short-circuited wire can make popping, cracking, or sizzling sounds.

How to Fix Your Microwave’s Noises

Having a noisy microwave can be incredibly annoying. So, how can you stop your microwave from making noises when it’s off?

You can fix your microwave’s noises by checking the magnetron, power supply, fan, or diode and replacing or repairing these parts if needed. Keeping your microwave unplugged may help, but contact a microwave technician if you’ve tried these solutions and your appliance is still making noise.

I’ll explain these solutions in more detail below:

Check the Magnetron

If you suspect that your magnetron is making noises when your microwave is turned off, you’ll need an ohmmeter to check its functioning. An ohmmeter measures an appliance’s electrical resistance. You can buy them online or in DIY stores.

However, before measuring the electrical resistance, you’ll need to discharge the microwave’s capacitor so that you don’t damage the other parts in the microwave or get electrocuted. The capacitor stores electricity and runs the digital clock when the microwave is not in use.

Here’s how to discharge your microwave’s capacitor:

  1. Unplug your microwave.
  2. After opening your microwave, locate the capacitor (the capacitor is not always in the same place, so you’ll need to consult the appliance’s user manual or look online).
  3. With an insulated screwdriver, touch one of the capacitor’s terminals.
  4. Drag the insulated screwdriver across to the other terminal to create a short circuit and discharge the electricity.
  5. You might need to repeat this a few times until you hear a loud pop indicating a short circuit.

After discharging the capacitor, you can check the magnetron:

  1. Place the ohmmeter between the magnetron’s two terminals.
  2. Using the lowest electrical resistance setting on the ohmmeter, check the reading.
  3. If the ohmmeter reading is less than 1 Ohm, the magnetron is functioning correctly.
  4. An ohmmeter reading of 1 Ohm or more means that the magnetron needs to be repaired or replaced and could explain why you hear noises when your microwave is off.

Check the Microwave’s Fan

When your microwave’s fan isn’t working correctly, it could be because of regular wear and tear or dislodged food.

Here’s how to check your microwave’s fan:

  1. Unplug your microwave, and discharge the capacitor.
  2. Remove the fan motor cover (most microwave fans are at the back).
  3. Check the fan for damage or food debris, and rotate the fan manually to see if it turns freely.
  4. Use a multimeter to check for electrical current. If the multimeter doesn’t detect current, the fan motor is broken and must be replaced.

Inspect the Diode

A microwave’s diode usually lies next to the capacitor and is a dark-colored and tubular-shaped part.

When you open up a microwave, you can usually tell immediately if the diode is defective because it will look cracked or blistered. It will also make a humming sound.

If you’re unsure whether your diode is defective, you can check it using the following method:

  1. Unplug your microwave and discharge the capacitor.
  2. Using an ohmmeter, measure the diode’s electrical resistance by setting the ohmmeter to R x 10,000.
  3. A normal electrical resistance reading for diodes is between 50,000 and 200,000 Ohms.
  4. If your diode is reading outside this range, you’ll need to replace it.

Unplug the Appliance and Check the Power Supply

If you believe that your microwave may have a problem with the power supply, unplug it and look at the power cord and plug. If you notice any exposed wires, a frayed cord, or burned parts, your microwave might have an electrical problem. 

Stay close to your microwave while it’s unplugged and wait to see if the noises go away. If so, you might consider leaving your microwave unplugged when you’re not using it to prevent it from making noises.

Contact a Microwave Technician

If all else fails, and you haven’t been able to resolve your microwave’s issues on your own, it’s time to contact a microwave technician.

Before doing so, it’s worth checking whether you have a warranty that covers the cost of faulty parts and a technician’s services.

How to Prevent Your Microwave From Making Noises

I’ve explained what issues can cause microwaves to make sounds when off. If your microwave is currently in good condition, how can you prevent it from making noises in the future?

You can prevent your microwave from making noises by using a plate cover and cleaning it regularly to avoid a food build-up. If you notice any problems, address them as soon as possible or consult a microwave technician.

Microwaves are low-maintenance appliances. You can keep them in good condition and prevent them from making noises by avoiding food build-up on the walls and in the fan. Using a plastic plate cover is an excellent way to keep your microwave clean, but you should also clean it regularly to help keep it working efficiently.

If you notice that your microwave isn’t working efficiently, fix the problem promptly or call a microwave technician.

Final Thoughts

Noisy microwaves can be annoying, especially when they’re off, and you’re not expecting them to make any sounds.

If your microwave is off but making noises, it could be due to any of these issues:

  • Hot parts
  • Faulty fan, magnetron, or diode
  • Transformer working continuously
  • Power supply problems

You can resolve these issues by unplugging your microwave or replacing or repairing the faulty parts. Consult a microwave technician if you’re not confident fixing or replacing the broken parts on your own.

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