 It occurs in almost all electronic devices and can show up with a variety of other effects, such as impurities in a conductive channel, generation and recombination noise in a transistor due to base current, and so on.1/"f" noise in current or voltage is usually related to a direct current, as resistance fluctuations are transformed to voltage or current fluctuations by Ohm's law.There is also a 1/"f" component in resistors with no direct current through them, likely due to temperature fluctuations modulating the resistance.