I've figured the problem. The glitches appears only in full screen mode. It's like screen crashes for 0.01 second every time, but in windowed mode all's fine. And no, I couldn't catch it with a screenshot. Also in full screen mode I get square resolution with black lines on the sides, like when you run a PS1 game on a wide screen or something. I don't know how it supposed to be, but my default resolution is 1600x900