Hello
I use a program called NeatImage,
www.neatimage.com. Download it and see if you like it. Nontheless, I've seen several pictures that turn out pretty 'neat' with grain in it
Maybe you're going at this the wrong way. Instead of trying to clean up the 'mistake', try to exaggerate it? Find a pretty cool picture, add more grain to it. How does that turn out? Maybe change some colors too? I'm just thinking out loud.