Theres known issues supposedly with the cam phasers going bad rather quickly on the 6.2s Causing knocks at start up. Someone on another forum im on described it as sounding like a diesel tractor idling in the cold. But apparently its a very common issue no ones been able to solve. Some have said even after having them replaced its not long before they go again. Dont know if thats your issue too but just what ive seen stated elsewhere.
Cant remember where ford cuts the warrantys off now. But might want to check with them if your still under it.