Burst noise

It consists of sudden step-like transitions between two or more discrete voltage or current levels, as high as several hundred microvolts, at random and unpredictable times.

Each shift in offset voltage or current often lasts from several milliseconds to seconds, and sounds like popcorn popping if hooked up to an audio speaker.

[3] No single source of burst noise is theorized to explain all occurrences, however the most commonly invoked cause is the random trapping and release of charge carriers at thin film interfaces or at defect sites in bulk semiconductor crystal.

In cases where these charges have a significant impact on transistor performance (such as under a MOS gate or in a bipolar base region), the output signal can be substantial.

These defects can be caused by manufacturing processes, such as heavy ion implantation, or by unintentional side-effects such as surface contamination.