You should be able to locate the source of the noise with an auto stethoscope. Just touch it on the the compressor and near the idler pulley, around the front of the engine. Closer you get the louder it will be.
If you doh't have a stethoscope a long extension will work, however, stethoscopes are inexpensive and widely available.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas