Have you guys notice that how the rear seat vent works? When you started your car and car was moving, did you notice that vent is always blowing? OK, I just notice that my rear seat vent just keeps blowing when my car is moving. Especially, it is loud as I hear when I turn off my radio.
Check this thread Rear Seat Ventilation? | PriusChat I posted the description from the owner's manual how this vent works. After you read that you may want to check whether the noise you hear is from the climate control vents (then you could just change the mode of climate control you use if noise bothers you) OR if the noise comes from the battery vents which may indicate your battery temp is high (which depending on your driving, you might want to have the dealer check out).
As stated above, turn your climate control fan completely off and chances are your noise goes away. The HV battery fan only comes on with battery temps above 95F and then has six speeds. With mine up to speed mode 4 my wife could not hear it standing by the rear door and she can hear a pin drop. If you are indeed hearing the fan making a lot of noise I would get it to the dealer to check out.
I don't know which of the six fan speeds was triggered, but I've heard the battery fan kick on while driving on a summer night. My first thought was the right rear window was open. Then I realized the source of the noise was lower at seat level. Also, it was a rather unusual sound, as if the fan blades were rubbing across a thin layer of fabric.
you may want to check the fan to be sure it isn't rubbing anything, although some have reported fans louder than others. i have never heard mine in three different prii.
