Technical description
Transformation is often accompanied by a distinct noise--an 8hz pulse, repeated five times, with each pulse lasting a roughly equal amount of time, whose pitch can be represented by the absolute value of a declining (for alt-mode to robot mode) or increasing (for robot mode to alt-mode) sine wave. In the G1 series, the sine wave generally increased when a Transformer changed to his robot mode, and declined when he converted to vehicle form (or whichever mode was smaller/shorter.) In general, the larger the robot, the deeper the pitch of the sound, and the longer the duration of the pulses. There is no general consensus as to what onomatopoeia should be used to represent this sound.