Cant aim straight...

Hey guys, I am having an issue with keeping my gun level.

If I try to keep my crosshair on the horizon while panning left or right, my aim moves up and down in a sinusoidal wave pattern. I can feel it fighting me to keep my aim level. Even in the firing range it is impossible to keep my aim straight.

I have two mice and they both have the same issue. This is not an issue in the menu of the game itself, or any other program.

Does anyone have any advice? (Mouse and Keyboard) PC

Thank you