Here's the outcome: "replaced engine lifters at both banks, performed oil and filter change."

Again, thank heavens for the warranty. I wonder what this would have cost out-of-pocket.

I'm happy with the dealership's service shop -- the repairs are (so far) flawless, and if anything the engine now has little more "go." Still, interesting to note that it took 10 business days to fix, most of that waiting for parts.

Any ideas what would make the value lifters problematic after ~ 25K miles?