[bmw1999m3]

I am hoping someone can tell me what this noise is. I think it may be a dying alternator but I am not sure as I haven't ever had an alternator die before. The noise happens on a cold start and starts to go away as I rev the engine and it heats up.
https://youtu.be/rS5rfbQNanw

 

[bmw1999m3]

EDIT** Fixed broken video link
https://youtu.be/C2F3DnolUoI

 

[wavewuver]

Try turning off the AC and see if the noise goes away......could be the AC compressor.

 

[E36-M3]

Did you ever figure it out? I have the same issue.

 

[rrsperry]

Belt tensioner, or idler pulley.