Again, thanks all for willingness
& again, according to your given opinions/answers I must have explained it all wrong.
I'll try once more:
1. The original shots were taken in 2 consecutive days, without the camera
over stressing/heating itself (total of 12 shots all together)
2. I could not upload the original PEF files due to size limits, therefore I croped
a small area out of them (something like 15% or so), than manualy, using PSP12 brigthen them a bit (Well maybe more than a bit, but both with the same brightening values), Converted the files to JPG and uploaded them without any JPG compression at all, namely 100% save of the original crop.
This is the reason that when examining the EXIF data, both attached examples seem to have the the same time & date.
3. I know all about exposure compensation, and that it actualy means increasing ISO value, and I dont complain about that, nither about the fact that there's a certain amount of noise in pictures, I complain about the fact that since both shots were taken with the same camera, with almost idetincal lighting conditions, & almost the same in-camera settings there is such a major difference in noise level.
Furthermore the 2 attached examples, are only symptoms to a phenomenon that I can't explain nor control in real life shooting.
The noise level of output shots from camera vary so much, even in the same
shooting session (I just could't find more examples in such a short notice, therefore I've attached only these) and it drives me crazy !!!!