Stutter when second monitor is connected

Hello.

In the process of making a game I noticed stutter when things are in motion.

It's very noticeable game stutter that happens at regular intervals. It looks like frame drops --> back to normal --> frame drops --> back to normal. But fps is rock solid 60.

I assumed that there is something wrong with my code. But after optimization same thing occurs. So i made simple scene with cube animation and stutter is still there.

After long search for solution in this thread somebody mentions dual screen setups and problems with refresh rates. So I disabled second monitor (tv actually) and viola stutter goes away. Does anybody else have this issue and knows how to fix it ? Turning vSync on/off does nothing. Changing graphics card drivers from latest beta to stable also doesn't fix this problem.

This is happening on Radeon HD 6670. Here is simple scene when this occurs.