I don't have any idea exactly what this would be. I will say, however, that my '05 is as creaky as any vehicle I've ever driven or ridden in. I can't tell where it comes from, there are just squeaks and groans. It was a big let down- even with over 100K, my '00 Explorer was as solid as could be- no squeaks, etc.
Mine doesn't creak at all, BUT it makes a very scary noise when I drive up a ramp (like into a drive way) with the wheels turned all the way to or near to the stop.
wwashing - same problem here, just don't pin the wheels against the stops. It's the metal stops rubbing between the frame and suspension. Apparently, you can grease this but I haven't.
Unholy - I don't have a problem with noise in my 07ST and I'm ready to roll over 12k miles. Definately time for the dealer to investigate.