I have been having a clatter noise coming from the engine when it is warmed up. The noise doesn't happen when the engine is in neutral, it needs to be motion and the sound starts out around 2000 RPMS. I have changed the EGR valve and the PVC valve. I have been reading on this site for a while and I am thinking maybe it could be a spark knock. Not really sure though I have been all over the engine looking for something that is loose and I can't find anything at all. I also removed the hoist brackets b/c i thought they were slapping up against the engine.
I have a 4.2L V6 '99' F-150 which is a 5-speed. I have around 85,000 miles on the engine. Thank you for your help
Cufan97

 

I don't think it's a spark knock anymore. It only happens when the truck is warm and if I give a lot of gas the clatter goes away.

 

I just bought a 98 F 150 with the 4.2 V6, 5 speed manual tranny. It only has 53 K on it. The truck is like new and I got it from a friend, so I did not even drive it before I bought it. As I was driving it home, the motor sounded a little noisy to me. I have been around cars all my life and I'm 64, so I'm hoping that what I think I am hearing is not true. Are these v6's noisy critter's? Somebody say yes, cuz I'm feeling kinda sick.