I've been battleing this same problem.
Took it in to the Ford dealership since its still under warranty when it first started happening. They were set on the struts needed to be replaced. They offered to order me some new ones under warranty but told them to wait because I had my BAT struts coming in. Replaced struts, still squeaks.
Took it back to them and they said it had to be the sway bar bushings. They ordered some for me, replaced my old ones...still squeaks. Made no difference what-so-ever.
The next step, they pulling the gas tank on Tuesday because they think its a baffle thats causing it.
2x95se: thanks for the suggestion on checking the back seat hooks. I'll get them to check that on Tuesday.
-neal