Well, the dealer 'did their thing' (inspected the noise) and reached out the other day with the following:
"We suspect the noise is due to excessive rocker play, which could be serious or not that bad. Worst case, 2 new heads, cams, and all of the rockers, lifters, etc. or best case, just new rocker arms. We need to tear it apart to see the extent of the damage, and that cost is $1,560. This would be applied to the repair cost."
Today they reached out and let me know that it needs all new rocker arms, lifters, and one cam.
Add to this that I asked them to check all fluids and to change the oil (They also discovered the mounting plate for the filter is jacked up) the total cost was just over $4,100 plus tax and it will be finished next Wednesday.
I was able to get them to agree to $4,100 out-the-door.
It's not cheap, and I'm not thrilled about it at all; but at least the top end will be new w/ a 2 year unlimited mileage warranty.
The only real question is, "Did I cause this, or was it already failing when I bought it?"
I'll probably never know for sure, but I do know that if we had bought one with lower mileage (at about $4K more), it could have still happened.