I'm having something VERY similar, it's not tearing... I have VSYNC on, I have FPS limited to 30, I have all the normal fixes but this terrible flickinger of the screen and flashes. Sometimes the bottom half of the screen would change to gray between flashes.
This started, for me, literally 3 days ago just out of the blue. I had not modified any settings, .ini tweaks, etc,. but had installed a mod here and there. I removed ALL mods and problem persisted...and then I noticed something VERY perculiar.
It only seemed to happen on one of my characters.
So I kept investigating...ultimately I stopped playing that character and switched back to another....and then noticed again, something perculiar.
When I pulled out my torch and walked around....and then DREW my sword out, the screen would flicker around just like it would with the other character, until the sword was fully drawn (hear me out, I know this sounds far fetched). I played with it over and over, and sure enough only when I drew the sword out, AND was holding a torch.
Additionally, the problem seemed to happen, occassionally, when standing NEAR those large cauldron's full of coal that have fire on them (all over skyrim and in towns). I don't know what they're called, but the primary thing to consider is FIRE.
So....my other character that this always seemed to happen on, is a Destruction Mage...his favorite spell.... FLAMES and FIREBALL. I loaded up the character and started running around, screen was "tearing" and "flickering" like crazy. I then changed to a different spell (or put my hands away) and the problem stopped.
Whenever I see the flame shader, the problem seems to come back. Oddly, with my fighter, I mostly only witness the screen tear when carrying a torch during animation for drawing my sword, like seeing the TOP of the torch causes the flickering.
But again, this only started happening about 3 days ago. I have removed ALL mods and refreshed my install AND reset my .ini files and cannot get the problem to go away.
-MM