Start Up Engine Noise PLEASE LISTEN

[986Porsche986]

I noticed last week that my 2002 "S" 52K miles (changed the oil about 800 miles ago , 0W 40W) started to make a "knocking" noise that lasts about 15 seconds then seems to disappear when I start it up. It seems to do it if the car has been sitting for a day or so.. I was finally able to get a vid with some sound bites.

If anyone is kind enough to download and tell me what they think, I would be thankful. Also, when I shut down, the engine has always made this sort of
just "stopped dead" klunk noise. I bought the boxster two years old and it
has always sounded like this. is this a normal shut down noise for a 3.2L boxer engine?
Here are the links to the videos, they are MP4's but any media player should play them.

here is the first start up on Saturday, cold engine, has been sitting for about three days. At about 10 seconds through 23 seconds, you can hear the
knocking noise that worries me.

http://rapidshare.com/files/103686095/boxster_startup_01.mp4

(7 MB file)

then the second startup, on Sunday, cold engine, you can still hear it but not
as much. It sounds to me like it is coming from the engine, and not the exhaust
as I first thought.

http://rapidshare.com/files/103687669/boxster_startup_02.mp4


third video is a series of shutdowns. does this sound normal to you guys?

http://rapidshare.com/files/103686530/boxster_shutdown.mp4

(1 MB file)


thanks for taking the time.