It looks mostly like scanner abberations.
When you scan low density films much more light is passing through and hitting the sensor thus bringing out any abnormalities that would not be visible with a "normal" negative. You have not said if this is visible to the naked eye or not. If not - i would say this is a scanner issue.
This happens on Imacons when dust settles on the bulbs thus creating similar "banding". this is much more pronounced when the negatives are out of range, and can be seen in any scan (even the cleanest most calibrated imacon or other scanner) when the range and threshold are pushed to the limit in photoshop.