Screeching sound after picking up car from oil change

So I picked up my 2008 Prius from the mechanic this afternoon. The only thing they did was an oil change and 27 point inspection. The form says they checked but did not fill any fluids. They did fill the tires. And also they checked a bunch of components. 10 miles into my drive home and right after making a turn and going up a slight hill, the engine started screeching something awful. Never in my life have I heard a car make that noise. It sounded like it was coming from under the hood. I pulled over and called the mechanic and let him listen to it before turning off the car. He asked me to turn down the fan to see if the sound went away or changed but it didn’t. It didn’t come back on when I turned the car back on. I’m taking the car back tomorrow but any ideas what it could be? Unless it’s the coincidence of a lifetime, the mechanic did something that caused this, but what? Never had any trouble with this car and the mechanic said the car was in good shape. They are Toyota specialists and have solid reviews.

 

Turn down the air. I switched it to the lowest level and turned off the A/C, didn’t help. He thought it might have to do with the air filter, I think. I might have misheard, it was pretty loud and I was a bit alarmed.