Update re: visit to dealer service and the shop foreman there this AM: Though the sound was far from its most prominent this AM (the gods apparently like to have a chuckle whenever I take a vehicle in for something like this), he was able to hear it, and he described it back to me just as I'd heard it, too. He is taking the information and will be contacting various and sundry folks over the next day or so and then getting back to me with a plan. He also seems to think it's likely associated with boost/induction/etc., but didn't pooh-pooh the story about the gearbox rebuild another forum member (that's you, 1FH!) is about to get due to transmission failure being associated with this. He doesn't seem to think it's particularly serious, but he's taking it for prompt action/investigation, and he's ruling nothing out at the moment, and for that I'm also very pleased and happy. Ford, at all levels, is impressing me at the moment with its customer service. Best I've ever had.