I dont know if anyone else has noticed this but when i select reverse it seems as if an extra fan comes on, its very noticeable as a passenger !! Could anybody suggest why this is ?
It could be automatically putting the air con on recirculation so the fumes you 'reverse over' don't get sucked in.
My passat does it but its not something listed in the manual, it also does it when you use the windscreen washer squirty so you don't smell it. The fan sound changes and sound slightly louder.
Hope this helps...