This noise you say you're hearing is your IMRC flaps in the ports of your intake manifold. This can easily mistaken for valvtrain noise and is a common problem with the duratec 2.0/2.3's...my car did the same thing as well. The flaps get sloppy in the ports of the plastic manifold and make a tapping/fluttering noise when they are closed at idle. Then tend to go away when revving the car or driving. Ford does not offer replacement flaps by themselves, you have to buy the whole intake manifold (about $250 if I recall). And unfortunately, the manifold you buy will eventually have the same problem years down the road since they are made from plastic!

 

Are you familiar with the mechanic's stethoscope or screwdriver trick? Use that on the valve cover to help give you some peace of mind. If it's the "tumble flaps", then you won't hear anything in the valve cover. Yes, it will take another intake manifold to fix it- unfortunately. I purchased a used one for mine. You can remove the tumble flaps, but be prepared to suffer low end torque loss as a result. The same goes for aftermarket manifolds, and cams are too expensive to help alleviate the issue of low end torque loss.

 

OH, btw, mine has been clacking for about 50k miles, and I'm at 150k.

 

Buying a used manifold might be a ok option if you are lucky enough to get it from a super low mileage car or if you plan on selling the car soon. Otherwise it is a gamble since you don't really know how worn it is....could last 6 months, or a year or so if you drive the car a lot and you plan on keeping the car for a while, buying a new manifold makes more sense since you know its brand new and should at least last for a couple years. Whynotthinkwhynot is right about the stethoscope thing, I forgot to mention thats how I found this issue with my car....put the stethoscope on your intake manifold right about where the port is... you will definitely be able to hear it over anything else..