I hope the metallic whirring sound has been sorted on your 40D. I've had mine a year now with no issues, other than a bluetooth disconnect problem which BMW have fixed. My fan too overruns with plenty of heat and sometime smell being expelled. I design feature of the engine I understand. The only gripe I have is the overstated fuel economy figures which BWM publish, which was one of the reasons I bought this car in preference to an Audi Q7. Not a concern if you are a US driver (still equivalent to 40p per litre there!), but we're somewhat sensitive to fuel prices here in the UK (GBP 1.38 per litre). My 40d averages 27 mpg on a combination of country roads and motorway each day.

Otherwise the car performs very well and is great to drive, with great torque and superb road holding and no understeer. Off for 2 weeks in the South of France next month, so will give it a good trial on motorways and mountain roads.