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Every motor makes some noise while running. The catalogue's general series noise reference is roughly 58–75 dB(A) and varies with power, number of poles, fan and frame. What matters is the character of the sound and whether it changes over time.
| Sound | Possible source |
|---|---|
| Steady, even hum | Magnetic field; normal operation |
| Air rush that rises with speed | Fan; especially noticeable on 2-pole motors |
| Growling, grinding, ticking | Bearing wear, contamination or grease problem |
| Fluctuating hum, whine rising with load | Phase imbalance, low voltage, loose connection |
| Squeal, knocking | Belt slip, coupling play, fan rubbing on the cover |
To trace a new noise, it helps to run the motor briefly uncoupled from the load: if the noise disappears, the source is most likely the driven machine or the coupling. As bearing noise progresses, temperature and vibration rise too. For choosing a quieter motor, see the article on motor noise and vibration.