Recently my 2001 X5 w/ 110k has been intermittently making a whirring sound, it sounds like a fan perhaps. The sound starts quietly and slowly gets louder over about 30 seconds and then dies down, when it is at it's loudest it can be heard from pretty far away. I have not noticed the sound when the car is moving and it seems to only happen when the car is stopped and idling (in neutral or park) .. It is so hard to have a mechanic diagnose because it is so intermittent.

I'm wondering if it could be the bearing on the electric clutch fan but I am pretty stumped.. any ideas?

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