Looks like a scanning problem. I have been encountering this as well myself. The easiest way to tell is to turn or flip the negative and scan it again. If the artifact turns up in the same place on the image, it is the negative, if it moves after turning, it is the scanner.
I have a HP flat bed that loves to do this on my large 6x9 color negatives. its a real hassle and requires going into separate channels to clone out the different colored streaks.