[335xi]

Because of the following reasons, I always thought it was the Vanos.
It has an oscillating high/low note.
It's always louder when I first start the car
Only happens in the winter with colder weather. Noise is not present in weather warmer than about 70 degrees.
As the car warms up the loudness of the noise dissipates and eventually disappears.
The sound seems to emanate from the driver's side head of the V10.

Sounds like Vanos, right?
Well, yesterday I was getting fed up with it and I wanted to record it so I could post a recording here but in order to get a clear recording I turned off the heat. Well, guess what? That made the noise go away.
Turned it back on, the noise came back. Off, noise went away.
So, why does the heat make such a racket? I had the 'snowflake' A/C button off so it should have been quiet.
I am very happy it's not the motor.

 

[mdyaman]

be interested to know what it turns out to be

could be the A/C blower or something that needs cleaning/replacement.

 

[335xi]

So, no one knows what this is? Do your M5s have the same noise when the heat is on?

 

[Misterfive]

I get the same noise. I think it's the blower motor

 

[335xi]

Does the noise oscilate?

I get the same noise. I think it's the blower motor

Sounds like low groan high groan, low groan high groan, low groan high groan

 

[MKballer]

Does the noise get a bit louder when accelerating from a stop?

 

[tdotM]

Funny, I just experienced that noise today. Pulled into the garage and turned off the engine but wanted to run the fan in Rest mode as the kids were asleep in the car. Heard the exact noise you described when I opened the door. Definitely not the engine since it was off. I turned off the Rest mode and the noise stopped, so definitely coming from the Fan.

 

[335xi]

Hmm, I don't think so

Does the noise get a bit louder when accelerating from a stop?

That would be hard to hear since the motor makes more noise when accelerating. I can only hear it when the car is idling stationary.