Noise is a very broad term that can be applied to a number of AC power line disturbances. Lightning surges or any other sudden changes in load, such as switching motor loads or power factor correcting capacitors can produce voltage spikes and ringing. Phase controlled rectifier loads and arcing devices produce continuous noise unless adequately filtered. Noise sources are either of common mode, which appears between both sides of a power line and ground or of transverse mode, which appears from line to line.