Hi I did some searching and did not find this particular noise. Both in a rented 2009 Prius, and the used 2001 I recently bought, I hear this high pitched sound. I would almost call it a "singing" sound. I doesn't sound like a problem - it actually is a pleasant sound, but I'm wondering what it is. I notice it at about 40 mph. If I had to guess, I'd say its from the transmission...
The Inverter (power electronics that produce the high voltage AC drive for the Motor-Generators from/to the 200v battery) works at a high audio rate. You can hear the first few harmonics of the current being switched in polarity at this rate. It also can be heard when listening to a weak AM radio station as noise when either braking (regeneration current) or accelerating (Drive current to the motors). JeffD
i can hear a prius from a block away.. it's the inverter.. that distinct high pitch wine is very audible at certain speeds. it's louder on the lexus models...