I just got back from having the service done. The tech wasn't aware of the service bulletin, so I was glad I put the number right in the service request. We did a quick drive around a bumpy loop they have and he confirmed the issue and proceeded to perform the procedure in the bulletin. He confirmed the rattle was gone afterward and so did I when I picked up the car. He found that while the 4 bolts were not loose, they had not been torqued to spec, so no charge for getting the work done under warranty.
However, I had a 60 mile drive home and I took back roads. I noticed that about half-way home the noise started to come back just not as bad as before, along with a creak when turning the steering wheel at low speeds. I suspect that to really solve it, you'd probably want to put some force on the different subframe pieces while torquing the bolts (for similar reasons as why you want the car resting on the ground at normal ride height when torquing down suspension bolts), but that's not mentioned in the bulletin.
In any case, my main concern was that the noise might have been caused by something loose in the suspension, which is now ruled out by the fact that just torquing the subframe bolts at least temporarily eliminated the noise. I'll add the rattle to my short list of things with the car that I'll deal with myself when I get a little free time (the others are the rattle above the driver sunvisor and the driver side rear seat rattle).