Finally took this into the dealer. They had it for two full days. They tried swapping on some Sahara tires, rebalancing my tires, driving it "in the air" on a lift to isolate the noise. (Yes, they could hear/feel it, too.) They also drove some other JLs on the lot, and they report that other JLs have the same sound, only less noticeable than mine. In the end, they conclude that it is just the way the JLs are and there's nothing functionally wrong with it. It just "does that."
Do we have any recourse? This seems like a design flaw of some sort, like I heard about the jiggly hoods on the JKs, for instance. It's just really odd that it's only in that window from about 63-67mph that you notice it.
Is "Jeep Cares" on here?