PD VRS estate.

Ive become aware of a hissing sound inside the car when the aircon is on. I know the aircon is working harder now that it is a bit warmer but I dont remember it being this loud before. Could this be a aircon fault developing and if so what causes it ? - loss of refridgerant maybe? The aircon appears to be working OK though in terms of cooling though.

Its done nearly 18K miles and Im sure the variable servicing indicator will flag up soon.

Had a similar issue with the AC in a Seat leon. Had it checked by a couple of garages and they found nothing wrong. Unfortunately I ended up listening for it all of the time and got tuned in to picking it up. Solution was - turn up the music.