A hum or buzz from your ceiling fan is the most common complaint arising from ripple control, which is generated when a transformer or the motor windings in a switched-on appliance resonate with the ripple control frequency, usually between 300Hz and 1300Hz. The noise is often, but not always, intermittent depending on when the ripple control signals are being transmitted. People often notice it most acutely in the night when off-peak hot water systems are turned on. Ripple control is a way in which electrical companies use a superimposed frequency on standard 50Hz AC power supplies, which are commonly found in most (if not all) Australian households. Simply put, electrical companies are controlling and managing off-peak power loads on their distribution networks. The frequency is used to control hot water heaters, street lights and water pumps through their remote receiver to control the power going to and from each utility. Ripple control may also be used to signal high network load periods for major customers to allow them to reduce power consumption. Ripple control and electrical harmonics noise is not the result of a mechanical fault with your ceiling fan. As such we do not cover either occurrence under our warranty. Where ripple control noise is found to be at fault, the customer will have to acquire a filter and have it installed by their electrician at their expense. If you make a warranty-based service call and ripple control or electrical harmonics noise is diagnosed as the problem you may be charged the call-out fee for the electrician.