Originally Posted by Vaughanabe13

A "highly charged capacitor" is not correct, but it is most likely an issue with one or more capacitors. Ceramic capacitors are piezoelectric so an applied voltage will cause mechanical strain, and thus audible noise. They probably used ceramic caps with a high dialectric constant and these are affected by temperature so the ambient temperature in the car and the temperature on the ECU board will likely effect how much you hear the noise. The noise could also be harmonic distortion from a capacitor that has a rapidly changing applied voltage, such as a switching power supply.