I just had my 04 fx4 in service for a month for this same exact sound. They told me cam phazers. Does the sound go away about 2000 rpm? Cam phasers generate the sound till about that level. Otherwise it also sounds very close to a collapsed chain tensioner, whish is also very common on the 5.4s.

 

that was my truck on the tube, i took it to the shop and got the cam phazers and soilnods replaced and it still knock after that it started run rough and so i took it back.
they ended up takeing the motor out and a part and repaced oil pump, cam chains,guides,tentioners, eny thing that was worn and it still knocks and run rough when hot at 900 rpm ish it starts to clap

 

Could be the cam phasers... My 5.4L sounded like a quiet diesel and after doing research here, I figured it was the cam phasers. Luckily I have a mechanical breakdown rider on my auto insurance. The dealership replaced the cam phasers and checked all other related parts. $250 later (deductible only thank goodness) and my truck sounds like it did when it was new. Good Luck.

 

I read on another forum that tapping was fixed with a coil pack and spark plug replacement. Don't know but the guy said it solved the problem when replacing the lifters didn't.

 

mine used to rattle and tap like crazy, at start up and when warm and running.
i started changing the oil every 2-3000 miles and started running a qt of marvel in the oil. its quiet now even at start up. i think it was just varnish build up in the lash limiters and tensioner.

 

That definitely sounds like a Phaser. I have a similar tick, but not nearly as loud.

 

The guys at my shop are convinced that it is an exhaust converter. They want to cut it off and bypass the thing to see if the sound goes away. does anyone know if this will work.

 

I am going to change my oil with royal purple 5w20 a couple times to try and clean out the sludge. ( another quick fix) I just dont have the money right now to put 2000 bucks into it. The mechanic just came over with the broken exhaust that made the same rattle when he shook it. We are gonna run a straight pipe for a couple days to see if that is what is causing the problem.

 

I have to say that the knocking stopped completely after the mechanics cut off the exhaust converter and welded on a straight pipe. I was having a loud knocking/ pinging sound on deceleration and at 1300-2000 RPM, the steering wheel would shake if I got over 60mph and the engine felt sluggish. I kept telling them that it was the cam phaser, but to go ahead and cut it off to see if that was the problem they could always weld it back on. To my supprise there is no noise, no shake in the steering wheel and no sluggish feel in the accelerator. they were even kind enough no to change the oil like I asked them. The 7 qts of Royal Purple and filter was about 80 bucks. Maybe this might help some of you that are having the same problem and may have changed the cam phaser with no relief in the noise. Hope this helps