Bob I have a 1999 F-150 with the triten 5.4 I had the plugs changed out at about 130,000 ran fine then I just felt it was time.It seems I lost gas milage when I did....could be just me.I have 189,000 on it now with no problems. They say you need to make sure the engine is cold when you change the plugs for they will twist off if they are hot. I have it done because I personally can't find the dang things.LOL As far as the sound your hearing I have no clue.