noise in cabin at tickover

[illavehalf]

been noticing a swishng noise on tickover that is noticeable inside the cabin ,,its not related to the speed of the engine as a slight raise in rpm is not changing the speed of the swishing noise , the noise is a reciprocal type as if something isrevolving and generating a noise , but i have noticed now that it is affected by putting on the air con and fan its not the blower fan thats noisy as its there when the fan is off but put on the ac and turn it off again and the noise diminishes /goes away its as if the aircon pump maybe but how can i clarify this??? any suggestions as i have asked before but not got to he bottom of it !

[dstev2000]

Could be the refrigerant boiling off through the evaporator behind the dash, that can produce a swishing noise similar to a fridge or freezer sometimes. If you turn the A/C off (Econ on in some models), does it fade and go away after a few seconds?

Increased noise at the evaporator can be a sign of refrigerant shortage which will be accompanied by poor cooling. If the A/C works well there is nothing to worry about.