high-pitched squeal on start

Sometimes when I start my 2021 Prius Limited, there's a quite loud quite high-pitched squeal. So jarring my first thought was some kind of anti-theft deterrence. But thinking it more likely it had something to do with the sound system, I tried turning off the audio system (which I've had set to an FM talk station) before turning off the power button, and in a half-dozen starts since I've been squeal-free.

The squeal is so unpleasant I don't look forward to the next phase of testing where I'll go back to leaving the radio on when I turn off the power.

One thing that puzzles me is that after purchasing the car used I'm pretty sure I left the audio on when powering down a good number of times before the squeal started.

If I have to always turn off the sound system before turning off the car I will be annoyed.

 

Thanks bisco, I will.

But no luck so far; I resumed leaving the sound system powered on on shutdown, and no squeals so far on about 4 startups. Unfortunately/fortunately.

 

OMG that's utterly pathetic!