The popping sound produced by an external camera flash is primarily caused by mechanical vibrations resulting from the charging and discharging of circuit elements within the flash unit. Specifically, the high-pitched whistling noise during charging is attributed to magnetostriction in the inductor of the flyback converter. Additionally, the pop sound upon firing the flash is amplified when the flash is obstructed, likely due to the energy output dynamics. This phenomenon parallels the supersonic shock waves generated by flashtubes and thunder, both linked to rapid thermal expansion of plasma.
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Flashtubes produce an electrical arc flash contained in a glass tube. As the arc develops a supersonic shock-wave forms, traveling radially from the center of the arc and impacting the inner wall of the tube.
In the 20th century a consensus evolved that thunder must begin with a shock wave in the air due to the sudden thermal expansion of the plasma in the lightning channel.