BMW E36 Forum

Hello, I have a 1996 328is. Recently, I've had 2 times where I've started up the car and theres some loud whistling/wailing sound, so I turned it off, and then started it up again, and the sound was gone. It never did this before, sounds like a weird noise for my car to make. Any Ideas as to what it could be? or could be a sign of?

A loud whistling sound is usually air getting in or out somewhere it shouldn't.
Best thing to do is wait for it to happen again and find where its coming from.