Why do some hybrids make a whirring sound when braking?

Question

I understand that it is the electric motor running in reverse to charge the battery, but why does it make the high pitched whirring sound?

In: 2

Answer 1

I believe hybrids built in the past few years are required to make an audible sound for pedestrians. The sound only activates under 20 mph and the internal combustion engine is off. When accelerating you are more likely to have the ICE on versus braking when the car most likely have the ICE turned off and is running on battery / electric only.