Hi peeps. I wanted to post this to help anyone who's also tearing their hair out over coil whine.
If you're like me, you'll have done a bunch of research already to try and fix it: undervaulting, moving PC away etc. Nothing worked.
I then noticed when eiditng an old project today that there wasn't any coil whine. This got me thinking.
I uninstalled the latest version of PP and have since re-installed version 14.9 and IT WORKED! No coil whine. You'll need to follow this guide to open new project files in older versions(very simple to do).
I did some reasearch into 2021 v15 updates and sure enough, the marketing all screams 'speed' power' and so on, basically what's happening is PP 2021 draws more power from the GPU thus creating the coil whine, where as in older versions there was less power and therefore no whine. If you aren't worried about the minor speed updates and stock sounds, then roll back your PP version and edit in peaceful silence. Thank god for that.