It's not something I hear from the computer, it's only from the speakers or headphones.
It has occured 3 months before and went away after a week or two, it didn't always happen with the game.
I'm pretty sure it's happening because of high energy usage when playing EU4, i've pretty much only played Minecraft before and that doesn't use the GPU a lot.
Temperatures before starting the game: GPU: 48°C, CPU: 33°C
Temperatures after 10 minutes: GPU: 51°C, CPU: 41°C
Sorry for the late respond, I know that it isn't EU4's fault but I have no idea where to get support appart from here.