Any thoughts or experience? I have a 02 S4 that has had a troubling noise at cold startup when left sitting for 2 days or longer. It has made this noise pretty frequent since both turbos replacement 6k miles ago. Its a very high rpm , fairly high pitch lasting aprox 1 min, then totally quiets. It will not do this on warm start ups or cold daily start ups (maybe a couple of times cold) It sounds like a dentist drill, like a dry bearing. Any thoughts?

 

Could be the starter motor geting sticky when cold, you'll have to listen to where the noise is coming from with the bonnet open