I've got a jerk problem. (no sex jokes please)

Basically when I load a replay the 1st impact causes the game to jerk for a second then it's plain sailing. If the replay repeats it doesn't happen again, it's only on the 1st run of each replay.

My pc's getting 60FPS with shaders.

I've also tried running with every background app/service turned off & it's still the same.

Any ideas? I'm only asking cos I'm working on a video atm & ironing out that tiny freeze is starting to wear thin.

*EDITS*

Ah wait, I've found a way around it with my capture app. Still annoying though.