Softener emits a constant humming noise even when not regenerating.

How to Fix / Troubleshooting

Safety first: Unplug the unit before touching the transformer or motor.

Isolate the source:

With the cover off, plug the unit back in briefly and listen to identify whether the hum comes from the transformer or the drive motor.

Corrective actions:

If the transformer is buzzing loudly, replace it with the correct AO Smith transformer.
If the motor hums but does not move, the motor may be failing or the valve may be jammed; inspect gears and cam for binding.
Ensure both transformer and motor are securely mounted to reduce vibration noise.

Persistent hum from a stuck relay or board component may require replacing the electronic control board.