screech at start-up

99 996 I've only had this car for a little bit, so I've got limited data I get a screech during startup. Very distinct conditions. Seems to be first thing in the morning -- haven't had it do it any other time of day. Only after the engine fires up -- starter does its 2-3 cranks, then screech -- immediately stops noise -- runs great. Don't notice any other noise -- sounds good -- only have a running boxster engine to compare too -- but they are essentially the same. Start it any time during the day -- even if having sat for several hours there is no screech. appreciate any pointers thanks, Mike

This isn't specific to a 996, but whenever I hear a noise at startup that only occurs in the morning, I can usually relate it to morning dew or fog having settled on the belt(s) and pulleys. Do you park outside or inside? Does it get foggy where you park?

It most likely is the auxiliary air pump starting to go bad. It usually only runs for about 1 minute on cold startups.

the noise you describe sounds like your IMS chain tensioner is leaking oil overnight. A new updated tensioner has a preload spring to minimize chain "flap" until the tensioner builds oil pressure.