Mottling effect in sky background ruining my pictures

[stevek]

Hello folks,
An issue I am struggling with is the mottled effect I have in my RGB before combination with the luminance.  The luminance (4 hours of 1x1, 10 minute subs) does not show this mottling.

I have traced this right back and it is evident in the individual RGB masters after pre-processing (each 2x2 and 12 x 5 minute subs). Pleased see close-in attached crops of final LRGB image and a R master.   I use drizzle integration after doing a windsorised sigma rejection with everything else pretty default other than sigma that I  drop down a few tenths.
 
Is there something else I need to be doing in image integration?  Or is there a way to remove this mottling please?  TGV denoise in the none-linear state after LRGB combination is too late in the processing I think....  Will play around with this a bit more.  I gotta fix this problem.

May need to put this on cloudy nights but trying here first.
Thanks, Steve

EDIT:  The mottling is visible on the individual subs but appears completely randomly across the frame between exposures.  So why does integration not remove it?

EDIT2:  I also played with reject low and high structures in image Integration and had these numbers up to 5.  Put the mottled pattern is the same on the integrated output.  I'm beginning to think pixelmath?

[dave_galera]

Have you tried MureDenoise on the linear masters?
However don't think MureDenoise works with drizzle.

[stevek]

Thanks Dave, I will try it, I can try without drizzle.

However,  I used MMT as per this tutorial and it gets rid of nearly all of that noise in the combined RGB image.

https://jonrista.com/the-astrophotographers-guide/pixinsights/effective-noise-reduction-part-2/

[dave_galera]

MureDenoise is absolutely brilliant, have a look at https://pixinsight.com/forum/index.php?topic=9206.0