When your appliance is running on auto mode, it will automatically adjust to deliver optimal indoor humidity levels. This means that, when the sensor detects indoor humidity levels are lower than the target, it will automatically increase the fan speed to quickly return humidity levels to an optimal level. Note that for users who have not set their own humidity target, your appliance has a default humidity target of 50%. 

If you find the appliance too loud, you can reduce the fan speed to a lower level or use sleep mode.