I have the common knock and voilent rattle of the 5.4 once the engine warms up problem. Happens tipping the gas to 1000rpms and letting it go. Then it drops to about 300rpms and beats its brains out. There is only 64000kms on it and the engine noramlly runs great and has plenty of power apart from the normal ford ticks. Anyway, I purchased this truck from a used dealer in January with 60500kms on it in the area and probably paid a little more that average becasue of the great condition it was in. It was advertised in the window that there was factory warrenty remaing til 100000kms or 5 years. I figured that was sweet so i bought the truck. A month after I was backing in the driveway(wheels turned) and it started knocking/rattling, gave it a bit of fuel and it went away, but could be reproduced in same spot every time coming home if truck is warmed up good. Stopped at the local Ford Garage and was told that my warrenty was no good becuase there was no history on their computer, and I because i had none. Pretty crappy. So I called the warrenty manager at a dealer 2 hrs away. he said that if there is not signs of abuse inside the engine there should be no problem and it's not my fault. Really nice guy too! he also said to contact Ford Canada, but I probably won't, unless I have to.
So beware of buying used and have a history of the trucks history!
Will keep you posted in my effords to have it fixed.

 

I bought mine used with 22K on the odometer. Being I was buying out of state, I needed to be sure especially since this was not from a Ford Dealer. I emailed Ford prior to purchase and specifically asked about the warranty and puchasing used. The reply was that the remainder of the factory warranty was in effect immediately on purchase, no conditions associated with that. I kept that email with me when I went to get the truck especially since it was about 2000 miles away. I did have a few small things while under the original 36K warrant and there was never any issues for me.