Mk 3 1.2 16v , whoosing noise

[Loathingant]

I am wondering if someone can help me, my son has a 2012 1.2 16v clio and we have noticed a whoosing noise when we turn the engine off and when the bonnet is up. Its not noticeable when you are inside or outside the car when the engine is turned off. However, it is very noticeable when you have the bonnet up then turn the engine off. Its a very distinctive sound like there is pressure releasing from somewhere on the left of the engine as you look at it . The engine runs fine without any other knocks or whines and it could be normal for the car. We only noticed it when checking his oil and water levels but as I am unfamiliar with these engines I thought I would ask the experts

 

[Phenom]

I'm probably not going to be much help

Brake/clutch fluid still that side of the bay on a 1.2? any chance the cap or something is letting air out once the fluid has heated up?