I find my 08 "kind of louder than stock" too...fwiw.

 

I had a 2005 and now have a 2008 4.6 and I notice the louder exhaust as well as more power... I also noticed that the intake manifold site about 3 inches lower then my 05 in the engine bay.. which is why I cannot fit my volant intake on the new truck.

 

Just get a new CAI, the silencer doesn't really do much but make it whistle.

pg 117 should be where the belt minder info is in your manual.

 

exhaust is different than your 06. i can't remember the difference but the muffler is changed

 

07 they re-positioned the throttle body on the 4.6 which according to ford gave it a few more hp. i have a k&n 63 series on my truck. it sounds pretty loud. supposedly picked up almost 10hp with it according to k&n.

my truck compared to my grandpa's 05 feels much more powerful tho