One other thought I had. I had this happen on a door recently. The roller shafts were binding up a bit in the bracket where they're are mounted. I lubed each shaft using an aerosol garage door lube, which is available at the big box stores. It cured the problem. The roller needed to move in and out freely as the door moved up and down. It would bind up then suddenly release causing a jerky motion and a bang.
The other option, and I would do this if they were mine as I don't like side extension springs, is to change the spring system out to a torsion spring setup with a shaft, drums, cables and a torsion spring. You have plenty of headroom above the door opening to do this, takes about 14" of space. The door would travel up and down smoothly without doing what it's doing now.