Clouds is good if you need one abstract noise pattern. If you need realistic texture, go and buy iColorama. Export your artwork at the resolution you desire as PNG. Open it in iColorama (you may have to live with the max resolution iColorama supports; don't worry, you will realize it when back to ASP). Kill the image - adjustment>brightness 100%>apply. Make it not white: brightness or exposure. Say, 20% gray. Open texture tab and use any texture you want (there are hundreds and all very realistic). Use "raise" to avoid color. Play with them till you get the right texture. Apply. Save as PNG. Bring back to ASP as layer and make it overlay.
This is much faster than scouting internet for the right texture or trying to use ASP tools. And you won't need to create a large library of patterns in ASP too.