High-pitched squealing sound from passenger side engine bay?

I own a 2008 Prius with 281k miles. I've been hearing a strange high-pitched squealing sound after turning off the engine. It comes from the passenger side of the engine bay near the bottom of the radiator, lasting about 5 minutes. The sound starts off as a high-pitched squeal, then turns into a pure high-frequency tone.

Example 1 -
Example 2 -

I literally just pulled it out of my garage for the first time in a week since I had to replace the ABS Actuator. I got lucky with a $250 used one from Facebook marketplace. The ABS codes disappeared after I did the air bleed and valve learning through Techstream. Car drives fine now and the dash lights are gone.

Anyway, in the process I disconnected one of the hoses going into the heater core and ended up spilling coolant everywhere despite having it clamped down pretty tight with my vice grips. I re-secured the hose and when I was done replacing the ABS unit, I refilled with OEM coolant from the dealer. I put a tall funnel in the radiator cap and ran a plastic hose into it from the bleeder valve, then ran the engine for about 30 minutes while blasting the heat. Could it be that I still have air trapped in the system?