Jumpy gameplay in Far Cry 2 and other games

Whenever I play Far Cry 2 (and some of my other games, too) the game will skip frames every second or so. About every second, it will just jump ahead 10 or so frames, making the game look very jerky. I tried to record a video of it using Fraps, but I am unable to, because whenever I start recording, the problem goes away.What is causing my games to skip frames and why is it that the problem dissapears when I am recording in Fraps? Is it normal for games to skip frames like this?Thanks