Just to clarify, the Leaf does not use a vacuum booster brake system, it uses an electric motor built in to the brake cylinder assembly. There is a super capacity in the back near the charger that provides backup power in case of a total electrical failure. This is all documented in the service manual.
TurboFroggy wrote:More than likely this is the vacuum pump for the breaks. You can test this by going to a quiet area, like in your garage etc with the windows down. Then with the car on, pump the breaks with it in park, you will hear the buzz when the vacuum pump comes on then it will turn off when it gets enough vacuum built back up.
My Ranger does the exact same thing, but it is very loud compared to the Leaf's pump. There are a few videos of the Ford Focus EV that you can hear the same loud vacuum pump that is in my Ranger in the Focus.
Leaf SL 2011 to 2016, Volt Premier 2016 to 2019, and now:
2019 Model 3; LR, RWD, FSD, 19" Sport Wheels, silver/black; built 3/17/19, delivered 3/29/19.