Get a PS Audio Noise Harvester, they sell for $75 apiece (used). It plugs into your outlet only, no devices plug into it, and any noise in the line is used (consumed) to power a small light bulb. The more noise in the line the more it lights up so you can see when your refrigerator goes on or light dimmers are in use. The more devices you use, the better, it really lowers noise. THe noise harvester is not a meter so it will not give you a "numeric value".
