From time to time, after bringing an image from ACR to PShop, I'll notice some really rough noise in a sky. My 5D has been pretty good at keeping that to a minimum. So, for a while, it was just a bogey. Tonight I finally found it, in ACR. If I ran up the luminance slider for yellow, grey clouds would start looking like Rodinal on steroids. So, not knowing really what that slider does, I'll use it more cautiously. What I was after, in so much ranch land scenery, was a way to control yellow so it was there but not so dominant; a way to lighten it the way you can in PShop in the saturation panel. Clearly Luminance must be a different animal. Didn't think it would be like patching out in a gravel parking lot!
Are you sure it is noise and not posterization? Can you not use the saturation tab to cool down the yellow? In Photoshop selective colour would be helpful?