Yes, the old "Filters DON'T produce noise in the sky, photographers do" adage has been illustrated again
I would add, as it's relevant to the following question, the the more expensive filter probably DOES NOT have a nicer hue,
either.
Oh, wait! One more thing before that question: you should use noise reduction sparingly, as most such processes
de-noise everything, including detail you might want to preserve.
And lastly...
Q: Can you detail how you are processing these, and whether they are crops of a larger images?