[thstone]

I'm with Anker - sounds like a hydraulic lifter isn't being reliably pressurized.

Hydraulic lifters are wonderful - by using pressurized oil, they raise up and provide perfect valve lash (gap) regardless of temperature, age, or wear. Thus, valve lash adjustment is never required (unlike my air cooled 911SC which needs the valves adjusted at least once a year).

However, if the small oil passage to a lifter becomes partially or fully clogged (or the lifter itself becomes stuck), then the oil can't reach the lifter and/or it won't take up the gap - this results in a tap-tap-tap, tick-tick-tick, or click-click-click sound. It is usually most noticeable at engine start and may or may not go away as the engine warns up.

If this indeed the problem, there isn't much you can do about it without opening up the cam covers to get to the lifters. You can live with this but there is a possibility that eventually the gap will become large enough that the lifter is moving back and forth in the gap which could cause it to start to deteriorate and eventually fail. This will take tens of thousands of miles so don't worry about it happening overnight.

The long term question is whether a noisy lifter will be the first engine component to fail and cause the engine to fail or if one of the other 30 known engine failure modes will occur (before the lifter fails) to cause the engine to fail.

As Anker mentioned, you can try different oils/additives but if that doesn't solve the problem, then you can either live with it or open up the engine.

Can you record the ticking sound and post a video for us to hear? That would improve the certainty of this diagnosis by about 100%.