How To: Eliminate Banding From Your Scans
A lot of the time they can be reduced by making sure you have a spotless scanner, but sometimes I get a strip running down the side of my scans, in this example I have a faint red strip running vertical down the side of the image.
Lots of details can be found online as to why this can happen, and many different solutions, some may or may not work for you.
Im using a Epson V600 scanner.
Here is what I found