The one piece of gear you never knew you needed
I am talking of the power conditioner. A power conditioner will correct problems with power supply that introduce noise into your sound equipment. Wiring in a building might be bad, motors, compressors, thermostat switches, fluorescent lights, some incandescent lights, even the activities of the power company as they load balance the grid; all of these cause what we commonly refer to as dips, spikes, brownouts, surges that supply incorrect voltages and can disrupt the frequency, and phase, introducing harmonic interference into the power supply, which you will hear as undesirable pops, buzz, crackle or hum.
The function of power conditioners vary based on the manufacturer, but in general they should do the following:
Power conditioners are not surge-strips or multi-plugs. A surge protector usually only protects for overvoltages. A power conditioner performs the functions of a surge protector, while also filtering out dirt or harmonic contamination in the power supply. They come in rack mountable formats, but you can also find more affordable units that resemble a surge strip or a multi-plug. You may in fact want to consider this for your home theater setup also.