Lifter noise on a Boxster?

[Ronzi]

So, I climb in the Box last evening and crank it up. It runs like crap (missing, stumbling) for a few seconds, accompanied by a sharp metallic tapping sound. I shut it off and start it again. Same thing, but not so much missing. Again. Same thing. The fourth time the tapping is less. I decide to let it run. After about 15 seconds the tapping slowly subsides and the engine smooths out and runs normally. After 80 miles of driving, it is still running normally.
If it was a small block Chevy I would say it had a stuck or collapsed hydraulic valve lifter. Am I hearing the same thing from the buckets on the ends of the valve stems? I undrstand these are oil-fed to eliminate valve adjustment.
Has anyone else experienced this?