Do you really use Norton crap? You know their software is poor, right? Just seeing as how their update causes other programs to jerk speaks volumes about their quality.
And the "jerkiness" due to monitor synchronization... I don't know, but is that kind of like V-Sync?
I also notice your loop is kind of average. I made up my own fixed-rate function that locks FPS if you're interested to see it.
It kind of works on the principle to call back X times per specified time interval via a callback function, either via a global function or a class.