You can use the shadow pass, it includes all shadowa in the scene. Don‘t if that is what you are Loopings for...What do you need this pass for?
Apply the shadow catcher to what you want removed and change its mode to for compositing. I'm not at my PC so perhaps my answer on this thread will help. https://forum.corona-renderer.com/index.php?topic=19611.0
I saw the same noisy effect in all render engines I used when rendering matte shadow, maybe denoising will help.