I get the same noise on my 2010 Prius (and, by the way, we get 49.6 MPG average over 17000 miles) - My thought is that it has something to do with the electric motor - I hear it intermittently, both when applying the brake, which would activate the electric motor, and at other times (I've changed the display to show graphically the hybrid elements that are active in hopes of narrowing the possibilities for our next trip to the dealership. My concern is simply that this screech may be symptomatic of some problem that will manifest, and want to register my complaint in the event that this becomes a fact in order to hold Toyota's feet to the fire in that eventuality. With regard to your mileage: one must drive a Prius differently than one drives a Grand Caravan - jack rabbit starts are a "no-no", and coasting to a stop sign or a stop light so that using the brake is used only to complete the stop, using the Jake Brake (B) to slow you down rather than using the brakes, cruising at 65
MPH, rather than 75
MPH will combine to deliver the "green" feeling you seek.
