Weird screeching sound from car that went away when turned off

Basically I was driving my 2008 Prius that hasn't given me any problems. I have regularly changed the oil and keep it topped up after checking every 1000 miles.

Today has been the first day its been hot weather approx 80 degrees F. After about 5 minutes of driving all of the sudden there was screeching but kind of like a muted horn sound from the engine while i was sitting in traffic. It was more of an electronic sound rather than an analog sound of a fan belt or something.

I soon pulled over turned the car off and the noise hasn't come back on since after turning off/on, driving for several miles.

I checked the fan belt that is still there but I don't know what else to check? Any ideas would be appreciated!

 

The AC was not on as far as I know. It is possible because sometimes I accidentally turn on the AC via the controls on the steering wheel. I don't know for sure since I turned it off so soon there after.

that said IF it was the AC....what would have caused this?


EDIT: Also I need to leave so I wont' be able to reply or respond for 6 or so hours from now 4pm Eastern