Electric noise
Air pumping noise
Abnormal noise of the loosen components inside when appliance working
When you plug in the appliance, you could only hear electric noise, instead of a "bee" buzz.
When the appliance starts to work, you could not hear the normal sound of water pumping, but an air pumping sound.
Abnormal noise of the loosen components inside when appliance working, such as noise from pump, boiler, iron or the unit itself.
