I want to believe the idler arm is somehow involved, but I don't know the anatomy of an idler arm very well. I'm pretty sure I did not change it when I swapped out the bushings and tie rod ends.
Thanks everyone for all the ideas of where to look -- I just have to get through T-Day and then I can go spend some time in the garage to figure out what's what. Using Rusty's method, I'll check out every ball joint, every tie rod end, idler and pitman. If nothing there, then I'll look at the UCA and LCA bushings. And of course, I'll make sure nothing has become loose or cracked. If nothing there, I'll just take it all apart and rebuild it. More to come.....