Hasta La Motion!

I’ve been using the Furnace regrain node a lot on some shots and have noticed that it creates a noticeable blocks of grain texture where I have added grain to CG. It’s most apparent in the blue channel and leaves noticeable vertical lines in places. I took screen grabs and checked this in Photoshop to check I wasnt seeing things, and the pattern definitely repeats every 145 pixels vertically.
The issue is the same if I use sampled grain or a stock preset. It’s not anything caused by the CG as I have tried it over heavily blurred images also.
Has anyone encountered this and do you have a workaround, as I cant get my comps past QC with this issue.
Thanks in advance.