Hello Pieter, my name is ***** ***** I'll be happy to assist you with this issue.Does the sound return with other tasks running, perhaps Microsoft Office or something of that nature?
Over heating shouldn't cause a sound like that and neither should a fan. I would venture to say it's the graphics card - a short or bad driver. Do you know if your drivers are up to date?
Does it sound like this? https://www.youtube.com/watch?v=22b5fLzZLJY
I would also suggest observing your power settings. I would turn off any energy saving settings for your motherboard (this can be done in the BIOS) and also ensure your computer is running a balanced or max performance power plan (not energy saving) in Control Panel and Power Options.Do you turn your computer on/off very often or leave it running most of the time?
It could be a malfunction in the POST speaker. It is very high pitched and provides the beeps one hears when turning the computer on. This is typically easily unplugged but requires opening the tower.