Why is My Microwave Making a Loud Noise?

You thought you would have a quiet night at home, but when heating up some leftovers, your microwave oven starts buzzing, crackling, or popping loud enough to drown out the smooth jazz coming from the Bluetooth speaker sitting on your kitchen counter. What’s causing that terrible sound? Is it even safe to use the microwave if it’s emitting such a loud noise?

Most common causes for noisy microwave ovens

The type of noise your microwave oven is making can be a strong indicator for which part may be faulty or wearing out. These are the most common parts responsible for a noisy microwave:

  • Magnetron  – The microwave magnetron uses high-voltage to create the microwave frequency that cooks the food placed in the oven cavity. In good condition, the magnetron will emit a low hum during operation. However, if the magnetron is damaged or nearly burned out, it may begin emitting high-pitched sounds or growling noises.
  • Diode – The diode works in conjunction with a capacitor to power the magnetron. A defective microwave diode could be the real culprit behind a noisy magnetron.
  • Turntable Motor – One of the few moving parts in the microwave, the turntable motor rotates the appliance’s glass tray so the food or beverage is heated evenly. Over time, the motor bearings can wear out which can create a grinding or screeching sound when the motor tries to operate. You can often uninstall the motor by first removing the microwave’s bottom panel then unthreading the motor mounting screw or screws and detaching the power wires. With the motor in your hand, try turning the motor shaft. Is it sticking or difficult to rotate? Then the motor is likely defective and will need to be replaced with a new one.
  • Exhaust or Cooling Fan Motor – A cooling fan motor or exhaust fan motor (usually found in microwaves mounted over a range to drive a blower wheel to draw steam and smoke generated by the range’s cooktop through a charcoal filter back into the kitchen or to the outside of the home through a vent), can wear out in the same way a turntable motor can. You should remove the fan motor from the appliance and try rotating the fan blades or blower wheel by hand. If the blades or wheel do not turn freely, you know the motor has seized and will need to be replaced.
  • Blower Wheel/Fan Blades – If you’re hearing a scraping sound after pressing the start button on your microwave, it’s likely the blower wheel or fan blades have become partially dislodged from the fan motor shaft and are rubbing against the fan housing. You can try reseating the wheel or blades, but you may need to replace the component with a new one.

Using a multimeter to test microwave parts

The magnetron and diode can be tested with a multimeter to determine if the components have continuity – a continuous electric path present in the parts. Before you attempt to disassemble the microwave to reach the magnetron, diode, or any other component for testing or replacement, unplug the power cord. Since high voltage capacitors used in microwaves may retain a charge even after the power cord has been unplugged, it is recommended to discharge the capacitor immediately after removing the cover. You can do this by placing a screwdriver blade across each set of capacitor terminals (avoid touching the blade when doing this).

Here’s how you can use a multimeter to test a magnetron for continuity:

  • Rotate the multimeter dial to the lowest setting for “Ohms of resistance”.
  • Touch the black lead to one of the magnetron’s terminals and the red lead to the other terminal. The meter display should show less than one Ohm for the magnetron to be working properly.

To test a diode for continuity, you will need a meter powered by a 9-volt battery or use a 9-volt battery in conjunction with the meter. For the latter:

  • Holding the black lead against one end of the diode, touch the opposite end of the diode to the negative terminal on the 9-volt battery. Touch the red lead to the positive terminal on the battery. Keep in mind, the diode should only have continuity in one direction, so if the multimeter display shows no continuity, try reversing the diode so the black lead is in contact with the opposite end of the diode when touch the other end of the diode to the 9-volt terminal. If the diode tests negative for continuity in both directions or has continuity in both directions when the leads are reversed, the diode has failed and will need to be replaced.

Beware of microwave oven arcing

If you hear a crackling sound during operation, you should observe the oven cavity for arcing: sparks or flashes often occurring near rack supports. Arcing can be caused by a dirty wave guide or the exposed metal of a damaged interior wall. While a loose blower wheel or faulty diode will not necessarily pose any imminent danger when operating a microwave, arcing can damage the oven and the cookware so you should immediately shut off the appliance and avoid using it until the problem is fixed. A new wave guide can be purchased if necessary or, if the wall is chipped, you can buy special microwave paint to cover the exposed metal.

Always put safety first when attempting a microwave repair

Because of the high voltage and high current used by microwave ovens, be aware that repairing this appliance poses a substantial risk for injury or death if precautions are not taken. You should always unplug the microwave before you attempt any disassembly.  Since high voltage capacitors used in microwaves may retain a charge even after the microwave has been unplugged, we recommend that only experienced professionals access and replace internal components.

Find the right microwave oven parts with Repair Clinic

Replacements for those parts that can cause your microwave oven to become noisy, like a magnetron, diode, turntable motor, fan motor, fan blade, blower wheel, or wave guide can be found at Repair Clinic. All you have to do is enter the full model number of your microwave in the Repair Clinic website search bar to see a complete list of compatible parts. The part category and part title filters allow you to easily refine that list to find the exact part you need. While Repair Clinic stocks appliance parts that fit microwaves from top brands like GE, Samsung, Whirlpool, LG, Kenmore, Frigidaire, and Panasonic, you’ll want to make sure you’re selecting a part that is directly associated with your specific microwave oven model.

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