Why do character joints continue sway?

I have created a few cubes, each connected by character joints to test joints. One of the end cubes is kinematic, so the "limb" has a fixed root. The joints mostly work fine but when the scene is run i find that the joints continue to sway from side to side, sometimes even enough to lift up in the air.

I tried to dampen the joints rotation but it only seemed to get worse. I am not using any extra scripts with the joints. Is there a reason this is happening? How can I fix it?