My understanding and I’m not an expert is that at least with Porsches that have , hydraulic lifters, the majority of the hydraulic lifter failures are due to infrequent oil changes and excessive running temperatures. The loud ticking occurs on start up, because the hydraulic lifters cannot build pressure and pump up. The noise that you are hearing in this situation is from the increase in clearance in the lifter causing greater lash.

In other words it's like the valves are out of adjustment because the lifters don't let them open and close the valves as they should. That's how it has been explained to me. It would be nice it a real expert could explain this.