Go to Effects. Once you are there, go to the option “Make Noise”. Take your cursor and move the arrow on Color Saturation to 0. Then play with the Intensity(I recommend 64), this will determine how much rain you want and press OK. Next, go to Effects, go to blurs and click “Motion Blur”. There, keep the distance at 10 pixels and the angling will determine which way you rain will be going. After that, click OK. Now to put it on your comic, save it as a png, import it on your comic, play with the opacity. Vohila! You are done!=)