In an instruction booklet written in 2001 for a Boss guitar effects pedal it says:
Do not connect this unit to same [sic] electrical outlet that is being used by an electrical appliance that is controlled by an inverter (such as a refrigerator, washing machine, microwave oven, or air conditioner), or that contains a motor. Depending on the way in which the electrical appliance is used, power supply noise may cause this unit to malfunction or may produce audible noise. If it is not practical to use a separate electrical outlet, connect a power supply noise filter between this unit and the electrical outlet.
Since this effects pedal is a consumer unit, it follows that there must be consumer power supply noise filters available, but I cannot find anything with that name available. Do they exist?
Another question: does this mean that it's a bad idea to plug something into a multi-socket extension along with anything that contains a motor or inverter?