Why Your Refrigerator Fan Makes That Intermittent “Zzz” noise at Low Speed

Have you ever noticed a faint, rhythmic “buzzing” or “zzz” coming from your fridge when the fan runs slowly? It usually happens around a few hundred rpm. You may think it’s a hardware flaw, but more often it’s about how the BLDC controller manage low-speed operation.

At very low speeds, the controller uses current chopping to keep rotation smooth. If the PWM carrier frequency is fixed and relatively low, the motor’s magnetic components can produce a slight magnetostriction noise – that’s the periodic “zzz” you hear.

The good news: this can be solved without replacing hardware. One common approach is using randomized PWM carrier frequency (say, jittering between 16 and 24 kHz). That spreads the noise energy across a wider spectrum, making it less noticeable. Adding a low-speed current smoothing filter also helps, as does choosing a motor with higher inductance.

For some controllers, a “silent mode” can be enabled through software parameters. In our PCBA, that option typically lowers audible noise by around 8–10 dB – not a complete silence, but a noticeable improvement for quiet environments like a kitchen.

So if your fridge fan gets a bit chatty at low speed, it’s likely the algorithm, not the hardware. Small tuning adjustments can make a real difference.