I'm not sure my current issue is exactly the same as the screech-of-death being mentioned in here, but a few days ago when I was booting up, the Windows 10 intro jingle blasted at max volume with a loud ringing following. Luckily I didn't have my headphones on at the time. I yanked out the headphone jack from my STX and waited a bit. I put it back in and the sound was gone.
The only change I did to my rig recently was to clock my i7-2600K from 4.2ghz to 4.4ghz (at 1.3v both before and after the OC, no turbo boost). That was about two weeks before this incident. A month before the incident I upgraded from a GeForce 770gtx to a 1070gtx.
Oh and I turned the 'left' and 'right' mixes in 'Mixer' in Xonar audio center to max a few weeks ago. I've since reset them to what I believe is 76%.
I think I had this screech back in Windows 7 once while watching a movie in VLC. Not sure if my clock was at 4.4ghz back then (very possible).
I've turned off all windows event sounds and the startup jingle just to be safe. I'll probably update this post if it happens again.
[EDIT]: Got high pitch scream when launching spotify after starting up PC. My screech appears to only happen (rarely) on the first sound that is played upon a new system startup, so not exactly what others have been reporting (screech during youtube vids and such). I fix it by unplugging the headset for a sec.