Just an update to this, but it did feel like the tension was somewhat low overall, so when I trued up my rear wheel a week or so ago, I ended up just tightening instead of tightening and then loosening on the opposite side, and the sound seems to be gone for now. Hopefully I didn't screw up the dishing by doing that, but I'm new and not very experienced at wheel truing, so if it runs reasonably straight and doesn't have any bad hops in it, I'm happy ;-)