Sorry for the confusion. I wanted to say that 4.8is and 4.4 N62 have the same alternator. M62 has a watercooled alternator.

The noise is not there when running the engine without the belt, so it's not the fan.

Looking forward to see some N62 engine videos :thumbup:

By the way, today I checked it with a mechanic's stethoscope and can confirm that it is the alternator what is causing this sound.

Here's the video. I just uploaded it - https://streamable.com/t520h

I just recorded it with my cell phone right after arriving home from work. About 15 miles of stop and go traffic.

This was a brand new after-market alternator installed way back in 2011 and purchased from starterpros.com. No issues from day one to-date - no error codes (INPA/DIS/ISTA/BMWScan) and no whistling noise as the video attests to.

More videos when revving the engine. I listened to your videos and I think mine has a faint whistling noise but the original one before replacement had the same noise if not a bit louder- there was no cause of worry or alarm. Yours is very pronounced even when idling - I can not hear any whistling noise when mine is idling. I suspect whines when revving are normal pulley noises as my e39 does the same. Yours being much more pronounced, are your sure your pulleys are ok?

https://streamable.com/556s6

one more video uploading .....

Thanks. I think a faint whistling is absolutely normal.
Pulleys, belt and vibration absorber were renewed a few weeks before renewing the alternator

Ok, all the 3 videos uploaded:
https://streamable.com/sexjc
https://streamable.com/556s6
https://streamable.com/t520h