Please help with hiss & squeal after shutdown.

Just noticed in the last couple of days (hot days, 90+ degrees) that when I shut the vehicle off, even after short trips (10-15 minutes in town), that a loud squeak and squealing emanates from the car for several seconds.

My first thought was that the car was overheating (as it is similar to the sound my old neon would make when it overheats), however I do not have a gauge to check and no idiot light has come on.

A quick search showed that the original Prius has a known issue with the coolant heat storage (CHS) water-pump that sounds similar, but this being a different vehicle I didn't want to jump to conclusions.

Anyone have any ideas? Overfilled radiator, bad pump, etc? Any way I can verify?

All help is appreciated. Car is only a couple weeks old so everything should be under warranty (though the dealer is quite a trek away).

----Edited Below----

After more reading it sounds like the CHS issue is only present in cool weather.

My sound last for about 2.5 minutes and gets progressively higher pitched and less loud until it goes away. Definitely sounds like pressure being released (like a steam valve or something).

Its a gurgle-hiss and definitely does not sound like the typical clunks and buzzes I hear from the car.

Also, after waiting for the sound to go away I can turn the car on and let it sit for a few seconds, then turn it back off and the sound is back full blast.

I also captured an MP3 from my phone. There is an audible hum in the "foreground" that is not from the car, likely just from the phone. Sound volume is low, please turn it up to hear.

recording-20130625-181037.mp3 - Google Drive