Solved. I recently started learning Blender and I was playing with the Freestyle option with Suzanne. I would like to achieve a "hand-drawn" effect, so I added a 2D offset type modifier to Freestyle Line Style and a noise modifier to each of its parameters. The idea is that the lines should change a little over time. The problem is that the parameters are not affected by the noise and I cannot find the error. The rendered images are always the same, am i forgetting something?