I used a 3' extension on the socket & was able to get about a quarter-turn tighter, so we're not talking about a lot of play.
Rattle's gone, but now I have a new sound, kind of a metallic clinking, random, & mechanical sounding, almost like a baseball card in the spokes. I'm wondering if something got loose in the diff.
At this point I'm out of patience & will be taking it to a shop for them to check.