When I get on the gas hard around 3k Rpms the truck makes a clanking/rattling metal on metal noise from under my truck. Any thoughts on what to look at? Nothing looks wrong, gotten under is and looked and grabbed to make sure nothing is lose but I'm stumped. It also goes away after a few seconds of rattling

 

heat shield ??

 

but wouldn't is rattle the whole time?

 

My 05 did the same thing and it ended up being the iwe on both sides along with both hubs. The vacuum lines that hook to the iwe was split on the driver side.
Thats on a 4x4 of course.

-Stephen

 

or a split/broken vacuum reservoir- part of the battery tray... my sister just bought a 2007 5.4l and it was grinding...local garage replaced iwe's/ solenoid.. still grinding.. went to check it... pop the hood- you could here the hiss near the battery tray....