Great work!
I think the noise in the clouds is because of the fractal roughness setting (too high) I think, but I'm not sure. As I already said I'm not that good with cloud settings.
You might also try to increase the clumping of variation but you'll lose those fluffy small clouds on top so that's not a really good idea I guess
I suggest you isolate a noisy part with the crop-function and then do some tinckering with the cloudfractal.
