Well upon looking at the second 3D Mark demo, I noticed that there is an option which gives you sound... There are both "run 3d mark" and "demo" buttons on opposite sides of the wondow, and the demo button will give you sound... But in 3DMark05, the demo only showed the sci fi portion, and there was no forest or boat sections shown, though the credits rolled over a portion which looked like it might be from the boat demo. And both 3D Mark 03 and 3D Mark 05 have crashed on me a few times. And I still can't run 05 at 800x600.
We (I) have to make money too, so the free version is limited featurewise. Once you buy it (20$) you can change the resolution and test configuration - and see all parts with sounds... well worth the measly 20$ if you ask me :)