Videos with sound: https://youtube.com/playlist?list=PLZ2paM1dIENLmEo3DL7TOnSOWijOj4YFe&si=Ku0v_fv1VBl-e5Z- 2014 Prius Two, about 130k miles. Makes this noise often, idling and driving. Even while off if the key fob is close enough. There doesn't seem to be any real issues other than the sound.
Its your brake booster pump. Seems louder than it needs to be. I can hear mine sitting in the driver seat. Always comes on when I open the driver's door and will cycle on again after using the brakes a little bit. Its normal. What is not normal is if it cycles on when you are not using the brakes. That is a pretty good indication that there is a leak I swapped out my master cylinder (accumulator?) and it definitely helped, but I have read of others that had the cycling going on for years.
Monitor how often you hear the noise... Once you hear it more than once in a minute its time for a brake booster pump swap.
