Improper agitation can indeed cause uneven development around the sprocket holes, but this is usually limited to smallish areas around the holes. If the marks go all the way across the film, I doubt that this is the cause. Stress marks are a possibility. Strictly, these look more like overexposure than overdevelopment.(posted 9553 days ago)What camera do you use? You might try running a waste film through the camera. Leave the back open, and watch the film as you wind on, and then rewind. The film should, of course, run smoothly, without wrinkling.
Another possibility is that the film is getting crinkled as you put it into the spirals. Does it easily slide in, or do you have to force the twisting motion? Again, you can put a waste film in a spiral, and watch it as it goes in.
What is your development technique? Short dev times, less than around 5 minutes, can cause uneven development.
The photos on your web site (nice pictures, by the way) don't seem to show the problem. Perhaps you could put an example up; it would help with diagnosis. Reply to this thread if/when you do this.