Ok, rebuilt engine, after a couple hundred miles I start to hear a slight clattering noise while moving, not at idle. I had a problem once where the metal plate that covers the clutch (labeled with a red 1 in the photo below) had some space between it and the clutch and could move around and it would clatter. I figured that's what it would be this time, but when I opened the clutch I found this:
The plate can rotate a tiny bit independently of the clutch plate, and it has gradually beaten up the clutch bell (damage circled in red,) causing even more clearance which explains why it was getting louder. I have never had this problem. How does this happen and how can I fix it?