Why are my USB-C ports buzzing when used?

Your issue could be a ground loop issue. Basically the outlet you have the display plugged in needs to be using the same outlet power feed. This can be an issue if you have two outlets nearby each other but are powered by independent breakers in the panel. A second issue is the polarity of the cords need to be the same. This can be an issue when one uses a older two pronged plug

Which can cross the neural and hot lines so the connection between the two devices gets messed up

Then we have the ground service! Is your outlets properly wired? I would get a cheap outlet tester to be sure the outlets are fully wired, I've often found the ground wire in older homes is just not present! So people replace the outlet and leave it disconnected! Lastly, the buildings ground at the breaker panel is missing or worn-out as the grounding rods over time do break down!

here's a good basics writeup Homeowner’s Guide to Electrical Grounding and How It Works