Quote Originally Posted by AgX View Post
But can you imagine a user's fault to produce a regular pattern as described?
Possibly, if the film were removed from the backing paper and somehow pulled tightly in a roll, or rubbed over the edge of a rough surface during loading onto the spiral. Or even when removing from the spiral after processing. I have had very similar "user faults" when I first tried to process my own films many years ago.

It is often possible to see tiny scratches on any smooth or polished surface by reflected light which otherwise give no problems (e.g. cleaning scratches on lens surfaces which have no effect on transmitted light). I have handling scratches on quite a few of my older negatives, even after I'd realised the need for more care. Particularly when I used to store films in a roll.

Not suggesting that it is the OP's fault, but it seems harsh to find the manufacturer guilty without giving them the chance to examine the evidence.