My 6.2L has been making a slight knocking noise for quite some time now. I haven't really investigated it, because it was very faint and hard to hear. Lately, it's gotten a bit worse. Now it's starting to bug me.

I've narrowed it down to coming from the number 1 cylinder, I'm pretty sure, using the stethoscope method. It's not an injector, cracking the injector lines does not make the noise go away.

I first thought it was a lifter ticking, I've had that happen a few times. Usually a treatment of ATF in the engine oil for a few hundred miles makes it clear up and go away. Not this time. It's also louder than previous lifter ticks.

The other strange thing about this noise is that it sometimes goes away after warming the engine up. It's always present when the engine is cold, but sometimes after driving a while, I can't hear it anymore.

The noise seems to be coming from the top end of the engine, near cylinder 1, from the valley side. Can't really detect the noise from the valve cover area or the injector side of that cylinder.

Could it be a collapsed lifter? How do you determine if you have a collapsed lifter? Wouldn't that also make the engine run rough because that valve wouldn't be opening all the way?

The noise doesn't seem to affect the running of the engine at all. It's just an annoying knocking sound that I know should not be there.

Any other suggestions would be welcome.

Casey