@scholten sounds to me like your monitor is experiencing a form of coil whine. Usually you can decrease this by changing the GPU settings on your monitor. i.e. brightness, color temp, etc. Also, try different inputs and see if that makes a difference. If not, open it up and see if you can determine which coil (or other component) makes that whining noise. There is a possibility of decreasing it by using some thermal pads etc.
Once you know where the whine comes from, post some good images of that area with your question
Adding images to an existing question
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I have a Samsung Ultrawide 34" sold by Costco. The way I fixed it is to make my brightness 100% and then decrease my contrast. I'm normally a high contrast low brightness person, but the high pitched noise was driving me nuts. So This is my compromise and I hope it worked for you.
crwdns2934271:0crwdnd2934271:0 howard.jow crwdne2934271:0
You probably recently downloaded an app that is altering the microphone functions. Uninstall the app
crwdns2934271:0crwdnd2934271:0 Gloria Adejo crwdne2934271:0