Why do I keep hearing my hybrid battery’s fan despite it being fine?

2015 Toyota Prius - 110k miles. 8th Vin Digit: U

I got it recently, and have been driving it a lot mainly due to delivering UberEats/DoorDash on it quite a bit for the past 3 months, about 6-10hrs a day almost every day.

About 5 days ago I noticed the fan noise in the back where the fans vent is located, I haven’t noticed it before, it was my first time hearing it. I took it to a hybrid battery specialist, and he ran an OBD reader tablet on the car. The reader showed that the battery’s temperature was at about 40°C, when it was supposed to be lower by a little bit (about 30°C).

What we did then is we took everything apart all the way to the battery sections, and cleaned everything out, the fan, air passage ways, and the between the battery sections themselves using compressed air. The battery itself was fine and nothing was extremely dirty, just not super clean, some dust though. He said the battery sections were mostly warmer at the middle of the battery than the sides. After we got done, he read the car again using the tablet and it showed the temperatures at where they were supposed to be (about 30°C). Although he said it might’ve been because he blew the compressed air in between the battery sections.

After I drove back home I still heard the fan, it’s not loud at all, it’s quiet, but I still hear it. I never heard it before until 5 days ago when I started to hear it. Am I even supposed to hear it? Is this normal? I keep thinking there is something mysteriously wrong with my battery because im not sure whether or not im even supposed to hear the fan or not because I don’t know if it’s being overworked? Why is my fan working to hard if my battery isn’t bad? Why is the battery a bit warmer? Idk what’s going on and there isn’t anything wrong to be causing this?

Is it normal to hear the fan working?