Microwave Making Loud Noise

Since most of the microwaves we service are over-the-range models mounted above a cooktop, a sudden loud noise is often tied to the same fan system that vents cooking exhaust, though it can point to the cooking components too. The most common cause is a failing magnetron, followed by a worn cooling fan motor or a worn turntable motor. 

Common Causes 

• Failing magnetron. The magnetron generates the microwave energy that heats food, and as it nears the end of its life, it can produce a noticeably louder hum or buzz during operation before failing completely. This noise typically only occurs while the microwave is actively heating something, rather than continuously. 
• Worn cooling fan motor. Separate from any exterior venting fan on over-the-range models, an internal cooling fan keeps the microwave's own electronic components from overheating during use. As its bearings wear, this fan can start to whir, rattle, or grind, and the noise often continues for a short period even after you've stopped the microwave, as the fan finishes its cool-down cycle. 
• Worn turntable motor. The small motor beneath the turntable can develop a grinding or clicking noise as its gears or bearings wear down over years of regular use. This noise is usually most noticeable right at the start of a cycle, when the turntable first begins to rotate, and it typically doesn't affect heating performance at all, even though it can sound alarming the first time you notice it. 

When to DIY vs. Call a Pro 

You can safely check whether the turntable spins smoothly by hand when the microwave is off and unplugged, and listen for whether the noise happens only during heating, only at startup, or continuously, since that timing is a useful clue. It's also worth noting whether the noise comes from underneath the unit near the cooktop venting rather than from inside the cooking cavity itself, since that distinction helps separate a cooking-related fault from a ventilation one. Diagnosing a failing magnetron, a worn cooling fan, or a turntable motor issue involves accessing internal components, which is a job for a technician and not something to open up yourself, since microwaves store high voltage even after being unplugged. 

FAQ 

Is it safe to keep using the microwave if it's just making noise but still heats fine? 

A worn turntable motor or a slightly noisy cooling fan is generally fine to live with for a short while as you arrange a repair, since neither affects safety directly. A magnetron that's growing louder is worth having checked sooner, since it's typically nearing failure and heating performance can decline along with the noise. 

How do I tell if it's the magnetron or the fan? 

A magnetron issue only produces noise while the microwave is actively heating something, since it only runs during that stage. A fan issue, whether the internal cooling fan or the turntable motor, can produce noise at other points too, like right when a cycle starts or briefly after it ends. 

Does this noise mean the same thing on an over-the-range model as a countertop one? 

The internal causes, magnetron, cooling fan, and turntable motor, are the same regardless of installation type. The main difference on an over-the-range model is that a separate venting fan for the cooktop below shares the same housing, so it's worth confirming which fan is actually making the noise before assuming it's a cooking-related component. 

Why does the noise continue for a bit after I've stopped the microwave? 

This is normal for the cooling fan, which often keeps running briefly after use to finish dissipating heat from the internal electronics, similar to how some ovens run a cooling fan after a bake cycle. It's only a concern if the fan runs far longer than usual or never stops on its own. 

Is a magnetron replacement worth it, or should I replace the whole microwave? 

For an over-the-range model, repair is usually the more practical choice, since replacement involves matching the exhaust duct and cabinet mounting bracket, not just swapping in a new countertop unit. A technician can confirm the magnetron is actually the cause before quoting the repair. 

If the noise happens during heating specifically, or continues well past normal fan run-time, Boreal can pinpoint the cause and repair it safely, backed by a 90-day warranty on parts and labour.