In electronics, noise is an unwanted disturbance in an electrical signal. Noise generated by electronic devices varies greatly as it is produced by several different effects.
In communication systems, noise is an error or undesired random disturbance of a useful information signal. The noise is a summation of unwanted or disturbing energy from natural and sometimes man-made sources.
- via wikipedia
Lots of things can generate electrical noise. Some common sources are:
- DC Motors
- Fluorescent Lighting
- Radio Equipment (including WiFi & Bluetooth)
- Power Lines
- Welding Equipment
Electrical noise can be kept out of a circuit by using conductive shielding which is connected to ground. This electromagnetic shielding can absorb electrical noise and prevent it from escaping or entering a circuit. When a digital or audio cable breaks or wears out, you can usually see the shielding show through the cable's outer layer.
Electromagnetic shielding can also take the form of metal enclosures or 'cages' mounted directly on a device's circuit board as seen above.
Learn more about electrical noise by checking out these links: