This happens after riding the bike for about an hour. I've replaced free hub, greased/torqued the cassette interface several times, etc. These videos show what I'm up against.
Update: after more googlings on the topic, I found reference to the pins on the largest gear making noise after they loosen a tad, and found recommendation to specifically lube the pins. I tried this with some extra chain lube and it seemed to help, but I haven't ridden the full hour of hard mashing yet to fully prove it out. I suspect these pins are not supposed to be loose enough to allow this, if indeed this is the culprit?
Update 2: oil on pins was not a fix. but I have narrowed it down to the spline finger portion that tightens from the outside- the movement is occurring at this point and making the clicking. It appears there is slop between teh two diameters, and the fingers are pulling from the outside, but allowing it to "shift" and creak under torque.
I read somewhere that gen 1 of eagle had some tolerance issues- is this perhaps what I'm fighting?