As already stated, this occurs on various vinyls.
This is a possibility. I noticed that ever since I put a polypropylene flooring tile down in the shop (over the concrete), I get a little finger zap every time I touch the printer controls, stereo or metal storage cabinet. But, this fine banding problem didn't occur until recently, and the flooring has been down for about a year.
The printer isn't grounded other than the "ground" in it's power plug.
As the banding is occurring on all vinyls, I don't think this will help. (?)
*Added: The image below was printed at 720x720
If you are using Roland colors, try using the closest Pantone match, I was trying to match a light blue and kept getting banding and a grainy look, switched to pantone and it printed properly.