Hi, I currently own a 2005 Freelander TD4 and have a noisy heater when the vents are set to windscreen demist.All other positions i.e underfoot well etc all seems quiet.I know that apparently the aircon comes on as well as the heater if temp is above 5degrees so as to asisst the demist on the windscreen so I assume the surging whirring sort of noise is presumably from the aircon unit in the the lower passenger side of the vehicle.The aircon doesn't seem to be very affective neither so I guess it needs a re-fill. Will this also cause the noise that I am hearing or is their another issue? thanks