I have a 2003 mustang V6. I noticed opinion in the engine a couple months back I've been babying it and it's still there even though I tried premium gas octane booster everything I can think of I replace the PCV valve I replace the fuel filter. I took it to the shop and they said that they're not quite sure they think it might be valve play might be this it might be that the only thing I really heard was $8,000 and I was like oh probably not. So my friend said something about a timing chain but the shop said that the timing is controlled by the computer and that is probably valve play. I don't know if they just wanted the couple hundred dollars to diagnose it or what was the deal but I need some help please please please any ideas anybody