just bought a 99 f-250 last week.has 151,000 on it.i bought it as a fresh trade in.during the initial start-up it sounds like a diesel then gets quieter as it warms up until you cant hear it anymore at all.thinking maybe rods any ideas.this is the 5.4.(thinking motor was warm before test drive because i did not hear it then) any help would be appreciated.

 

For what its worth my old boss had this problem on a f 150 with the 5.4 motor and what he found out was that they were putting the wrong oil filter on. I now it sounds simple but its worth a try. He changed it to the right one and the noise went away.
good luck

 

thanks.had a motorcraft on it.now i am trying a fram but it still knocks.fom my research this seems fairly common on the 5.4