If your car sits out and there are any trees around, and when you turn on the AC it starts the whirring noise, it may be leaf litter in the HVAC fan housing. Sounds strange, but it happens. Take out the cabin filter and see if it's full of leaf junk. If it is, you may want to clean the fan housing. You can get some of this stuff from the filter opening. To get it all you have to remove the cowling and vacuum out the fan cavity. My XF sits out 24/7 365 and I have to do this every 6 months or so. Of course it is exacerbated by the fact that it sits under a huge live oak next to my driveway. It's not a very good design but it's not too hard to fix, just a pita.