Update for future reference: Lauren was right, it was the drop links. On inspection they looked fine, but as I had the car in the air anyway, I replaced them, and the noise has gone.
Surprised (and annoyed), as the old links looked and felt fine after removal...no splits in the boot that I can see, and they didn't feel too loose. I may cut the boots open later and check the rose joints.
And they are a pain in the arse to remove, even after only 6 months on the car. Still, preferable to having the strut assembly out.