Montreal's Metro old cars had a similar three-note signature sound. The notes have preserved as the "door closing" chime in the new cars: https://youtu.be/Hu_1JM_UiuA
I wonder what's actually making the noise. PWM on the transformer windings, or PWM on the motor windings themselves, or did they just use speakers? I have so many questions.
Overhead power lines are 15 kV, 16⅔ Hz AC in Austria; the drivetrain is of the variable voltage-variable frequency (VVVF) kind, and conversion to three-phase power is done using solid state components. Comments say these switching elements (IGBT or GTO thyristors) apply lower frequency to the motor at start, then gradually increase once it is in motion. So I'd say the "glorified coil whine" comes mainly from the motor windings.
