noise from air con after engine switched off?

noticed a strange noise about 10 mins after ive switched my engine off on my fabia VRS its a very faint beeping noise whcch lasts for about 5 secs followed by a kinda whoosh which lasts for about 3to 4 seconds, seems to be coming from the air con unit area but not sure definately, only noticed it after i had washed the car, obvviously didnt get water in the engine ccompartment, read somewwhere on here that the AIRCON intake is below the windscreen? maybe water running down the screen has gone in there

its not loud and probably would only here it with the bonnet up, hasnt seemed to do it only when ive washed the car, after coming back from a long run? sorry its a daft qquestion but was wondering what it could be

this is my first diesel car and first with air con, after owning a polo 1.4 , looking under that vrs bonnet is mind boggling, like that 1000 piece jigsaw i had when i was a kid.