I'm pretty sure I have that same clicking sound with my 3.0 litre. At one time I was sure it was the heater valve but I think I eliminated that as a possibility before. I usually have the radio loud enough that I don't hear it but I still notice it sometimes.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)