I've had my 2013 Prius (base) for almost a year now with ~18,000 miles on it. Today when leaving work to go home, I noticed that whenever I let go of the gas pedal so that the car is coasting and decelerating, there is a high pitched noise. The noise and frequency of the noise sounds very similar to Morse Code -- high pitched and not constant with no particular pattern. The sound seems to be coming from under the dashboard on the driver's side. No, it is not the standard odd Prius sounds. I turned off the radio and it was still there. It occurred in the parking lot, as well as the freeway, so speed is not a factor. Any ideas what this could be?
Sounds like your hearing got better. Normal sound for me, I can hear the frequency changing on accel and regen.
I have the same issue after 9 years from your post. Can you recall what the problem was and how you fixed it? Thanks!