A current spike, from off to Turbo always causes a voltage ringing
on newer driver designs R5 4.7Ohm were added and the 10uF cap moved behind it not connected directly to the battery any more
this is knows as a low pass filter, so only low frequency signals can pass, the higher they get the more dynamic resistance they have to pass
additional the MOSFET got on the gate a 47 Ohms resistor to soften the turn on/off switching point
making the time for the current change longer so also the ringing is reduced
Dels measurments of unmodded driver
basically any switching activity causes a voltage ringing, depends on many factors, but basically any conductor has some very very litte capacity and inductivity
I think first discussed here