Rav4 2018 high pitched noise, driver's side

[mkmig]

Hi!
I got a Rav4 6 months ago. 2018 hybrid with a low milage - all the MOT and checks were ok.
However, since the start, it had a weird high-pitch noise coming out from the drivers side. First, I thought it was the fan and ventilation but after checking, it's definitely not that.
It seems it happens when the car switches to EV mode and then back? However I don't know if that's just my supposition. It could be to do with ventilation and AC?
I left it at the dealership so they can have a look, and they came back saying that front and back brake discs are pitted and need replacing.
Now, they don't know if that's what's causing the issues though and second, if they are pitted wouldn't it show when I got the car?
I mean, can these discs rust in 6 months?

I've attached a link to the video when I recorded the high pitch noise - it is audible if you up the volume.
Has anyone had the same problem with the Rav4?