"Emergency Broadcast System" type alert noise when starting 2002 Prius

Been driving my 2002 Prius since January 2005 and I've never heard this noise. It first happened Sunday as I was driving down the road, then this morning (twice) as I started the car. It lasts about 15 seconds for several "rings" of a shrill, electronic (definitely NOT mechanical) sound that reminds me of Emergency Broadcast System tests on the radio, or a really annoying cell phone ring. No visual warnings or lights are displayed (well, the Check Engine light is on, but it's always on, and my local Toyota dealership has been unable to shed any light).

Any ideas what my car is trying to tell me? Searching has come up with nothing for me... there was one thread I thought sounded like parsley but the answer had to do with a rogue nav system & I don't have one of those.

I used the voice memo recorder on my phone to capture it this morning; will try to figure out how to get that posted here online later.

 

"parsley." PAYDIRT. thanks tons, autocorrect.

 

View attachment crazypriusnoise.m4a.zip

Here's the noise. Upon further reflection, the best way to describe the sound may be as the mating call of a demented electronic cricket. The service tech at the dealership where I dropped the car this morning said that to him it sounded like a bird chirping, but I don't know, I'd be pretty scared of that bird.