My car would creak at low speeds over road imperfections and speed bumps. I changed the sunroof seal(fixed wind noise), still creaking. I lubed all the rubber seals, doors/trunk, still creaking.

Then yesterday I pushed the hood with a few fingers very little force and there was quite a bit of play and it made noise.

What I did was add foam insulation tape(I doubled up the foam to make it thicker) to the contact points where the hood touches the rubber stopper in the engine bay and around the hood latch. Now when I close the hood there is no play and no noise. Drove the car around at low speeds and no noise. Basically my hood was creaking at low speeds because of the play. My car has 80k miles maybe the rubber hood stoppers just crushed down over time.

If you have the same symptoms or a higher mileage GS just press around your hood with a few fingers to see if you have the same issue.

 

I haven't looked at the GS 350's hood bumpers, but all the rubber bumpers I've ever seen are adjustable. Did you try adjusting them to put a slight bit of pressure against the hood?