The TechZone has posted part 3 on designing a $1500 audio cable. This time
they talk about noise.

The more commonly considered forms of noise are electric, magnetic, or the combination of both. When electric or magnetic fields are formed close to a potential receiver (i.e. the cables) they are generally considered independently. If, however, the noise is being generated far away, the two are considered together and called electromagnetic noise. The source of this type of noise is usually other electronic components or electrical devices or wiring.

High End Audio Cable Design - Part 3