I Belive It Is Coming From Under Or Around The Firewall Area,it Sounds Like A Clatter Or Ticking At Highway Speeds, Seems To Go Away At Lower Speeds Or Load.could It Be Timming Clatter ,got A 150 V/a Box.

Maybe this thread will help: http://www.dieselplace.com/forum/showthread.php?t=105481

I had a ticking noise coming from the underneath the dash on driver side. It took the dealer 3 days to fix. They said it was fuel lines vibrating against the firewall.

It has been driving me crazy for sometime now. My 04' made the same noise also. Seems it turns out that if you have a bug or rock guard on the front of the hood which creates turbulence and the vertical trim on the windshield goes ape. Some silicone sealer on the trim and problem solved. Now, if I could just find out what is making noise at my left knee level inside the dash I'd be a happy camper........