salnj, with a reading of 12.2v via OBC with car OFF, my 3.0d sometimes has problems starting, at 12.1v has major problems need to turn key to on then back to off then on again and works...

I get via the OBC test 9 car off & after sitting all nite:
12.2-12.3v

13.9-14.0v NO accessories on when driving

13.5-13.6V (with aircon on, radio on, high beams, biggest drop is caused when I switch on the fron fog lights )

unless you have a good mutlimeter dont bother with it , my mutlimeter was reading figures quite a bit higher than the OBC

PS that whirring noise unless it is a mssively loud noise of the main heater fan etc is the small fan behind the air con controls, its normal for it to spin until car sleeps, wait about 16mins (leave windows down and car in quiet location) you should here it stopped after 16mins

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E53 X5 3.0d SUV prod.date 11/2004 eng.variant M57N Europe Right hand drive N