Its more like a scream really, it happens when the car sits for a while (overnight) lasts only 10 seconds. I think its coming from the turbo. It only happens max. once a day, not necessarily when its cold out just when the car sits. I can leave it the rest of the day and start it again and it won't happen. This morning I noticed it made the car shutter and idle bad while the noise was going on. I have no loss of power or other noticeable noise while I'm driving.

Any ideas? Turbo about to go? bad cat? I really don't think its the belt.

 

Sorry, its a bone stock b5.

 

Its likely the secondary air pump underneath the airbox. Only runs briefly while the engine is cold.

Sometimes it can be cleaned out, sometimes it needs replaced. Makes the noise you are describing when it is bad.

 

Thanks, I will check it out