Straighten the pins out on the cages. They can get slightly bent from balls flying around on the playfield which will causes them to drag or hang up in the small holes they slide through in the playfield. Chances are this is the cause of your problem.

John.

He said you can hear the coils fire so I doubt the opto's have anything to do with it as it sounds like they are seeing the ball. He also said the cages feel tight when he slides them up through the holes. The problem most likely is bent pins or "nails" binding up through the little holes in the playfield when the coil tries to fire them up.