High pitched whine when engine on

I have heard similar sounds in more than one Prius, though hard to say from that clip if it is identical. I doubt it has anything to do with "nowhere to put the charge". I am curious, if you keep the hood up and wait for the engine to shut off on its own, exactly what sounds you'll be able to record then.

 

If the SoC is 100%, why is the engine on? How long was your downhill? Did you switch to HV or turn on the defroster? I don't know the answer to your question about the high pitch noise, but I am curious why your engine is on. There have been several 2021 PP owners reporting the engine coming on and not being able to start the car in EV mode even with 100% SoC.

 

The video, turn on the pre conditioner while plugged in and wait until it starts to quiet down after about 5 minutes. It might be a similar sound. The engine has always sounded louder to me during the breakin period when the car was new. Break-in period seem to be dependent on how many warm-up cycles the engine gets under it belt. It quiets down after it has been used for a while, at least it did for me the way I use the car. Cold / near freezing temps makes it sound somewhat louder especially when new. YMMV/..

It also makes a lot of weird noises. Sometimes even when it is turned off. Get used to it.

When Prime was first release in 17 there was a lot of discussion concerning the ICE switching on with 100% SOC while going downhill and in any kind of weather, not just when it's cold. Suggested fix was to stop plugged in charging so the pack had some extra room to accept the charge of the initial downhill.

It really bugged a lot of owners that lived at the top of a hill / mountain. A lot like how the ICE firing as the weather gets colder is really bugging a lot of new owners now.

There are probably other ways to fix at least these two issues by handling the car with kit gloves. It helps to know more about the car and why it does what it does when it detects the many combinations of limits and set points as programmed into the Prime by Toyota.

One reason PC is liked so much is that there are a lot of owners who want to know what the car does and why, as apposed to just getting in the car and driving it like so many other car on the road.

 

A mechanics' stethoscope is just a few bucks at the auto store, and is great for pinning down where odd sounds are coming from. Sometimes finding out can surprise you.