Originally Posted by blitzkrieg
From what you’re posting, the noise is the alternator. An overrunning “clutch” is used on the alternator drive pulley that allows the alternator to spin somewhat independently of engine speed. If the engine is revved up and shut down while at high rpm’s you will hear the alternator to continue to spin even though the engine is off. In other less complicated words...it's normal...
But the bearings in that pulley can go. As well as the bearings in the fan for the radiator.
Them being out of alignment or damaged may cause a high-pitched whine.
330xi SG/Terra/Burl -- ZPP, ZSP, ZCW, CA, Sirius, PDC