All stators will growl with some dynamic noises, but a 'Bright' pinging resonance when the alternator is conducting can sometimes be reduced by going to a different diode.
Often high current industrial diodes are designed with a soft turn on to extend lifetimes of all involved components so some cheaper diodes flash on all at once and the whole stator ends up ringing (more loudly) from it.
Sounds like you're talking about an "avalanche diode", where the current creates additional electron-hole pairs, allowing more current and reducing the voltage drop at high currents.
This increases efficiency by lowering voltage drop and the associated losses. But as you point out the sudden flip from just turning on at a higher voltage drop to turning full on in avalanche mode makes for an abrupt change in current, corresponding to energy in higher frequencies. When these get translated into torque by the reaction between the coil currents and the magnets you get to hear them.
Avalanche diodes are cheaper, not because they're crummier, but because there's a lot of 'em made. B-)
