There should be a check valve to stop exhaust from getting back to the air pump, that is usually what starts to fail and takes out the air pump. Mine was noisy but went back to normal (took a while) after replacing the check valve, but I'm talking 3.0L.

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