Hello, my name is Mark and I will try help you with this.
Can you tell me when the noise occurs?
Usually when starting , just a whooshing noise like the sea when car is cold when car warms up it gets better but doesn't go away fully
Is the noise there when the car is stationary or moving?
more so when moving
You need to check for any missing or poorly fitted grommets in the bulkhead. Check where any wiring or cables come through from the cabin to the engine bay.
is it a water build up somehere do you think or air in the heating system
I think it is more of an air sound. Air getting into the cabin because a grommet is either poorly fitted or missing.
will check it thanks