P7100 - Sharp but Noisy...

In good shooting conditions I have never had sky artefacts at base ISO with my P7100.  I shoot raw and then process in-camera later.  I find the in-camera processing to be excellent.

However, I did come come across similar artefacts on one occasion when having shot in low light, images were processed with a high sharpening setting.  When processed again with a lower sharpening setting the artefacts were nowhere to be seen.

I think your sky artefacts are probably due to over-sharpening.

I recommend you try the in-camera processing facility but whichever method you use, computer software or in-camera, keep an eye on the sharpening setting.