Same noise mine was having. Sounded similar to a ticking, like a sewing machine motor. When it was cold out it would do it more, now as the warmer weather is here, it's nearly gone. I was told it's the lifters sticking.

 

I also have a 2004 Expedition with the same knock..when you fixed the leak did the knock go away..I took it to a ford dealership and he said it could possibly be a spun bearing as well..

 

wow, that must have been some real knocking sound coming from the manifold

 

Knocking noise sounds like lower end Not. So I own 2003 and a 2004 Ford Expedition and both trucks developed a hard knock noise and I tracked the noise down to a more then except able source !!!! The noise on the 03 was the catalytic converter on the left side and
On the 04 it was on the right side. Both trucks same knock sound both trucks same
Answer !!! Wow. And to think two repair shops (one on each vehicle). 2 different estimates one for a trans and one for a engine rebuild. Lol. And turns out to be a 250 dollar fix on each truck so case in point don't just rush into a costly repair because some repair shop said you need to.

 

"Knock! Knock!"

Who's there?

"The engine in your Ford!"

 

A plug is backed out in one of the cylinders, possibly. Happen to me.

 

I had a ticking sound for 3 years that I thought was an exhaust leak. It would go away when it warmed up so I didn't worry about it. It blew out a plug when my brother borrowed it, after he fixed it the ticking sound was gone.


It would be worth checking to make sure all your plugs are tight.