Someone on a forum had a question about why horizontal lines might be showing up on their 3d prints. Someone else suggested that maybe their infill was showing through and that increasing the number of walls from 2 to 3 thicknesses might fix it. That’s a good place to start and I thought that was the solution to the problem.

Well, it didn’t fix it. It turns out that they had to go through their whole 3d printer. Their z rod had just a little bit of play in it. Once they adjusted that, the horizontal lines went away.