I've heard noisy lifters many times, and this is definitely lifters. But just based solely on the fact that the three sets of lifters I have tried are perfectly quiet on startup, while they are still primed, and the noise only shows up after there has been time for the oil they were primed with to be pumped out. This would lead me to believe one way or the other, not enough oil flow is reaching those specific lifters. This doesn't happen on every startup.. Only after I have swapped to a primed set of lifters. My question is more-so about how to check/fix oil flow issues in the head.