Canon lens with a catch
Well, I found out what the small bump was. By picking up the edge of the rubber focusing ring with a fingernail, and using a toothpick to roll it off about its own width sideways, I discovered that there are several small screws under the plastic ring that the rubber seats on. They are accessed through one hole in the plastic ring, and they seem to fasten the piece immediately below the ring to the piece below that. Two (of three) had come loose, and one had become cocked in the access hole, keeping the ring from turning at all. I got all three pieces lined up and started and tightened the screw, and thought I had it fixed. There was another screw loose, and since the ring was now free to rotate, when it went past the next loose screw, the same thing happened again. I lined it up and tightened it, and everything seems to work normally.
I can't wait to play with it...