Just had a issue with my car. Had a noise about 20 secs after start up. Went to ford thinking the worst and it turned out it was a loose harmonic balancer bolt. . The dealer had never seen it before and needed to call ford techs. They diagnosed it from experience with highway patrol xr6ts. Apparently it's quite a common thing with hwy cars due to high constant revs. At 2500rpm the noise vanished. If yours does the same then I'd be thinking it has the same issue