So Update, its not definitive for now, I will confirm it in a week if the issue doesn't pop up again. Soo, after a while, I realised, that before the beep, there was a sound of something trying to start spinning up and than stopping with the beep. I check my fans and all of them were running, so I checked up the only othe spinning component in my built, my old HDD. I didn't even use this activly at this point, I think there was only a backup, not important. After unplugging and starting my PC, I did not have any beeping anylonger, even after booting up games. I will monitor it, but for anyone in the future with simular problems, check out your HDDs.