Quote: "could have been screen tearing"
Screen tearing is an incredibly minor, barely noticeable effect that occurs for a split second when playing (fast) movies or videos (where you can see half of one frame, and half of another: normally only with fast movement occurring) - that's why V-Sync is used. There's absolutely no way in hell your problem is caused by screen tearing
Your problem is unfortunately very serious - or at least, I would bet it is, especially since the effect is not consistent (and the random pixels are clearly corruption - especially the black in the top right)
EDIT:
For reference, screen tearing looks kind of like this:
The problem corrects itself the next time a frame is drawn, provided there isn't a continual lag/backlog
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