In the last article I discussed about how the 5.4L variable valve timing works using VCT solenoids. I recommend you read through that article first before this one. Replacing the VCT solenoids will be the least intrusive first attempt in eliminating the noise and I highly recommend trying it first.
This article is mainly written with the 5.4L truck engine in mind, but it also applies to the 4.6L used in trucks, vans, and cars. VCT noise is a very large concern for most 3 valve owners. The engine is naturally very noisy, but sometimes it is extreme. One issue is a loud metallic noise heard when you let off the throttle. An easy way to tell if this could be your issue, then you must start and drive the vehicle until it is up to operating temperature. Stop and put the vehicle into drive while holding the brake. Raise the RPM's to 1500 and hold momentarily. Then release the accelerator pedal. If you hear a horrible rattle that sounds like your rod is about to go through the side of your block, then this is the article for you. Ford has released a Technical Service Bulletin linked at the bottom.
The very first thing to check is the oil level. Be sure that oil level is full and you used 5w20 weight oil at the last oil change. Also check to determine if the correct oil filter is being used. These engines do not like aftermarket oil filters especially on cold start up's. This would be an excellent time to go ahead and change the oil and filter to assure you have the correct quantity and quality of oil.
In the above mentioned TSB, it tells to replace both of the VCT solenoids depending on the results of your testing. To actually diagnose this issue, you need to have access to Ford's IDS (integrated diagnostic system). If you do not have access to these tools, you could take it to your nearest Ford Dealer or simply replace the VCT solenoids if you believe this is your problem. At this point, this is the cheapest possible solution to your problem.
They should be replaced as a pair, and can be found relatively cheap here: 5.4L Variable Valve Timing Solenoid.
Replacing the solenoids is easy on the 2004-2006 models. They are located on the front of the valve covers. Simply remove the oil seal with a pick, hook, or screwdriver. At the bottom of the well is a torx bolt. Remove it to allow the solenoid to be removed. You may need to replace the valve cover VCT seal after removing it. You can used an appropriately sized deep well socket to install the new seal.
To replace the solenoids on 2007-up engines, you must remove the valve cover because those oil seals are now inserted from the bottom side of the valve cover.Wow Ford, that was an ingenious move. It is advisable to replace the valve cover gaskets. You can use the article mentioned below as a guide to removing and reinstalling the valve covers.
For those unlucky ones that have replaced the VCT solenoids but had little to no effect on correcting the noise, it may be time to read up on how to go about Changing Ford 5.4L Phasers and Timing Chain. Your problem is likely deeper in the engine: having low pressure oil issues, broken phasers, and/or worn timing components such as guides and tensioners.
Related TSB 12-7-10.