Noise

One great way to examine images is to open in Photoshop, add a Levels adjustment layer, and play with moving the black and white sliders. I'd move the white level slider left, maybe around 220, and the black slider right. This increases contrast and lets you see blotches and uneven areas as well as dust spots.

Thank deejjjaaaa for your reply and guidance. I am attaching a crop jpg, straight from a raw file. One thing I noticed: if I put the white balnace eydropper on the white area the blotchiness goes so perhaps the artefact is related to that?

if you want to make a point then you shall provide a screenshot and raw file to illurstrate... otherwise it is just ~innuendo