Due to the electrostrictive effect of ferroelectric ceramics, when an AC voltage is applied, elasticity occurs in the lamination direction of the multilayer capacitor chip. Accordingly, the circuit board also expands and contracts in the parallel direction, and the vibration of the circuit board is audible as an acoustic noise.
Although the amplitude of the chip and the substrate is only about 1pm-1nm, the level of noise is audible.
There is almost no noise generated by the capacitor itself; however, when a capacitor is mounted on a board the vibration increases, and when the cycle of the amplitude reaches the audible frequency range (20Hz - 20kHz) of humans, it can be heard as a noise. For example, the noise sounds like a "hum," "hiss," or a high-pitched tone.