i have a 1999 5.4 f150 just had a spark plug blow out on tje #3 cylinder. took it to my usual guy and came back with a $500 bill :/ all new plugs and coil and rethreaded the head. i got it back today and notice a new sound and a more "under a load" idle and rev up along with the new sound of a humming noise. almost like a moving park in under pressure of some sort. any ideas i really would like to know i called him and told them about the new noise but he said its prolly nothing.....

 

Moved to 97'-03'.