Actually my first thought was to blame the camera. I used to have a camera where I had this issue but not the current one (EOS-3). I tested several rolls by scanning them before inserting the negatives into the sleeves. No scratches.
I like the idea given by Joe VanCleave, but I do not have that luxury.
Joe, do you know which ones are the top load sleeves? I want to try those, sounds like a good idea.