Some electricity suppliers in Australia offer customers different charging tariffs depending on time of day, for example, Peak hours (8am-8pm) are more expensive than Off-Peak (8pm-8am).
Suppliers can signal the tariff change to various devices (such as Hot Water systems to turn on) by using a feature called "Ripple Control" over the existing electrical circuits. Ripple control has been in existence for many years in Australia. Since our electricity supply is 50hz (50 cycles per second), the ripple control signal is sent at a different frequency (for example 400hz or 1050hz) so it can be easily distinguished.
The problem is that many electrical devices such as toasters, fridges, fans, fluorescent, halogen and LED lighting can be sensitive to the ripple control signals. This may lead to buzzing sounds from affected devices. In the case of LED lights there can be a perceptible flicker especially if on a dimmer circuit. Electricity suppliers can use different signals/frequencies at different times and therefore devices in one area/suburb may be affected whilst the same device in another area/suburb may work perfectly.
Modern dimmers from Clipsal and HPM will have ripple control filters built in to their circuitry to minimise the signal interference but may not necessarily be guaranteed 100% of the time depending on the supply area they are operating in. Usually if the problem exists, it will only be seem when the lights are dimmed. It is not common to see the problem at full brightness.