faint high pitch whine during braking

That noise is probably coming from the inverter, and is normal.

 

Pat is correct as usual, the whine also occurs during acceleration, but ICE noise covers it up.

 

The great thing about our Prius' is that they generate power during braking that's reused for accelerating later. Granted it's not super efficient, by the time it gets back to the wheels it may be as little as 30% back, but it's better than nothing.

When stopping traditional cars simply burn away all the energy from thier forward motion in the form of friction at the brake pads.

To reclaim power during deceleration our electric motor is used as a generator, the power is sent through the inverter and charges your battery.

You're hearing, ev motor as a generator,+ the inverter as a charger charging your batteries. It's a good sound.

My wife comments on the sound too, I don't hear it as much. It's a high frequency whine some peoples ears are more tuned to than others.