1997 Chevy Truck lifter noise

The lifters are hydraulic and when they get old, it takes time for them to pump up - meaning to work properly. This is probably the ticking or knocking you hear. When the oil heats up, it flows easier into the lifters - thus they pump up. However your lifters are by no means old. This does not mean that they cannot fail so make sure that the oil if changed every 3000 miles and put in SYNTHETIC 10w-30.I suggest Castrol Syntec or Moble 1. This may solve the issue.