Here's a larger view so you can see the extent of the interference. It was intended to be backlighting for a forest scene. First I used the fill tool in very dark green, and used the airbrush to brush long diagonal strokes over the top, in various shades, to give the impression of greenish light rays. Then motion blur was applied to help blend together. But the end results are pretty appauling. The motion blur only adds to the problem. But I still don't think this is normal; I also have a similar problem when using the lighting filter. Also, adjusting the levels feature adds further agravation. I tried using the noise filter as suggested above, but because of the severity of the pattern, I would have to use a lot of noise which looked worse than what we have here.