I noticed, a few months back, that one of my CZ's made a series of clicking noises when thumb cocking the hammer, as the hammer neared full cock. With my ear to the gun I could tell it was at the back of the frame.
Hammer spring coils "skipping" past rough spots on the hammer strut/spring guide.
Since then I've started polishing the corners of the hammer spring guides when I take one apart.
Not sure if the corners "wear" the inside of the spring coils or not, over time.
Not sure how much it actually would decrease double action trigger pull, if any, but it just seems like it would be a good idea.