How would this effect be acheived?

Ok after the page loads if you look below the content area there is a gray wave effect. Anyone have ideas on how to do that? I have most macromedia products at my disposal and 3dstudio max 4.2 with an arsenal of plugins. I thought maybe shape tweens but probably nto.

it just looks like shape tweening movieclips, but i could be wrong…I zoomed in and it looked like tweening.