I have a 2005 Prius with 57,500 miles on it. Some times (not all the time) I get a buzzing sound from under the hood at start up. This noise is a buzzing sound, not the usual whiring sound. This buzzing will continue until the ICE starts. It seems to happen more if the car has sat for a couple of days or the morning is cold. Once the buzzing has stopped, it stays stopped for the rest of the day. I do not think that it is the brake pump since it continues as the car backs out of the garage (on battery) and the brakes are off, but stops at ICE start a few seconds later. Could this be the inverter cooling pump? Thanks Dennis Edson
This is normal, it's the car pumping the coolant from the Thermos in fender to the engine. It will only happen if the engine is cold, and the thermos is still warm. (usually after a few days of non-use it will be cold)
