Didnt want to jinx it straight away, but a few days later, the fix is still good. Car is silent again. No more creaking or groaning over bumps and undulations. Feels a whole lot more sorted as a result. Previously, the Sydney dealers were just thinking it was door and sunroof seals, which have both proven to be furfies. Amazing how little things, once they've gotten your attention, can really sap one's enjoyment out of owning a car. Eagers Holden in Brisbane fixed it. Shout out to the foreman (Ben, I think it is) who had a great attitude and heap of knowledge. Exactly what you hope for when you're trying to get something fixed.