Undesirable random electrical transmission on network cabling that is generated by networking components such as network interface cards (NICs) or induced in cabling by proximity to electrical equipment that generates electromagnetic interference (EMI).
Noise is generated by all electrical and electronic devices, including motors, fluorescent lamps, power lines, and office equipment, and it can interfere with the transmission of signals on a network.
The better the signal-to-noise ratio of an electrical transmission system, the greater the throughput of information on the system.
You can generally reduce noise by using higher-quality components, lowering the temperature of components, or using shielded cabling. Be sure to locate sensitive networking components and cabling away from heavy machinery, generators, motors, and other equipment that can generate a lot of EMI. Also be sure to terminate cables properly at patch panels and wall plates to minimize noise due to crosstalk.