I have a brand new 2005 F150 Lariat 4x4 Crew Cab. I have put about 3,000 miles on it so far. Last week when I was driving down the highway all of a sudden this noise started that sounded almost like I had dropped my exhaust and was dragging it along the ground. It was unbelievably loud, and was coming from the engine. It went away after about 30 seconds. It has happened 4 more times since then. The dealer says "Nothing is wrong". This noise is so loud that people slow down and look at me on the highway. It seriously sounds like my truck is about to explode right there. I have never heard anything like it. Any thoughts??

 

What motor is it?
3 valve 5.4!

 

It has the 5.4L

 

next time u hear the noise pull over before it goes away and look for it.... and where exactly do u hear this noise?

 

I heard something strange on mine that sounded similar to what you are describing. I only have 350 miles on mine though and not even through the first tank of gas?

I'll keep an ear open.