My '08 X5 4.8i (04/08 manufacture date) does the same thing .... noise is primarily evident during cold weather (40 degrees and below). Noise will continue until the car is completely warmed up. By "warmed up" I mean that the interior temperature has reached 68+F. Noise seems to disappear after. I don't recall hearing it during the summer months ...

I suspect that it is an electric circulator pump that circulates warm engine coolant through the interior heater core until the thermostat opens ...

Try lowering the interior cabin temperature setting to something like 40F or less. If my theory is correct, there should be no demand on the circulator pump and therefor no noise ...

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PAX5
BMW CCA #20645