Ok, did some more searching leaving out any model or engine codes and came up with this video that sounds exactly the same.
https://www.youtube.com/watch?v=WzTTm_nD6ro
Comments show some other cars having the same symptoms - noise when warm only at idle. Looking like crankshaft damper. Rubber looks fine, but I can move it some with both hands. From the runout and stiffness, I'm going to replace it. $500 seems cheap insurance; if the rubber turns loose bad things can happen.
I'll report back if it solves the issue.