Lest you think the title implies trouble, let me disabuse you of this notion from the start :-)
Last month, Wentworth went in to get a little preventative work done, and also fix a potential problem, which was a rattle/clunk at low speeds over bumps.
The clunk was given the attempted fix of a 2008 engine mount Toyota service bulletin, but alas, after driving it home, it was clear the sound was still there. I thus wanted to bring it back to check it out, and at 40,000 miles, it was time for a tire rotation anyway.
Over the last month I've actually grown less concerned with the sound. It has been mentioned in PriusChat (one such thread here) by numerous people, which, at first glance, should be cause for concern, but with another look, tells me more that the sound is apparently a "Prius thing", and while not my favorite thing about the car, it appears that it has no adverse effects over the course of many years, despite its widespread presence.
Patrick Wong (incredibly helpful Prius guru for whom I have great respect) also told me that his three Prii over the years have done the same thing, and he hasn't been able to figure it out, and so just lives with it. If Patrick feels that it's fine and not a long-term issue, then I'm inclined to think along those lines, too.
I will update this is there is ever a problem, but for now, it seems innocuous, and the thing still gets me 70 mpg on occasion.
On another maintenance note, Prius owners, to keep rust off your infrequently used rotors, just shift into neutral while going down a hill sometime and brake nice and hard with no one behind you.
Tire rotation was $19.95, air set to 42 psi front and 40 rear, no other charges. I went to Premier Toyota of Newport again, much better experience than last time. More communicative, the tech went out and rode with me to hear the sound, and they followed up a couple days after to make sure everything was going well. Definitely feeling better about them after this.