2005 Ford F150 V8 Two Wheel Drive Automatic 64700 miles
About 1,000 miles ago, I noticed my a clicking or knocking sound coming from the engine area of my F150 when I first put it in drive after it has been sitting for longer than 4 hours. As I increase pressure on the throttle, the clicking sound increases in frequency. After about 1 mile or so of normal driving, the sound goes away completely, not to return again until the car is parked for several hours. My mechanic is confident it is not a loose exhaust bolt, and fears it is a problem with the oil lifters.
To try to solve the problem, I did a complete oil change, added oil stabilizer, and used lucas tune up in a can in a tank of fuel. That hasn't dramatically improved the situation, though the clicking sound is not as loud now.
If this is a 3 valve engine as I believe it is, there was an issue with the camshaft sprockets. The three valve engine used a variable cam in the heads. These cam sprockets are oil fed and would make noise when the engine was cold. There used to be a Service Bulliten out for them, but I don't believe it was ever a recall. I have seen them (on extremely rare occasions) cause damage to the lifters, and once caused complete engine failure (though Ford never admitted it was due to the cam sprockets). I would suggest, should you choose to have the noise repaired, only have the dealer perform the repair. It is very particular in how it is done and if done wrong, the engine would have to be extensively torn down. Hope this helps.