Hi Roger
Thanks for the links.
I problem I have is exactly the same problem you posted.
The cabin generates air pressure or a buffetting noise and this is because (as I have tested it) the air release values (or one of them) is 'flapping' as the air exits the vehicle.
These exits are located either from the boot or from under the corner of the rear bumper (one on either side). A bit tight to get to, but they are just in fingers reach.
I tested this by moving the car to a quiet location (preferably a garage), switching on the ignition, turning the fan on lowest speed making sure the fan was set on air intake and not re-curculate, closing all doors and windows and standing outside of the car near the corners of the rear bumper. You can hear the plastic rectangular flap quite clearly flapping about. By sliding your hand up between the bumper and car body you car raise the valve and this clearly cures the fault. Thing is, how do you cure it permantly?