Everytime I switch my car off, there is a strange bubbling / pressure escaping sound from around the header tank area, is this normal? There are no leaks, and the car is not using any coolant and the sound is only there after switching off

 

Normal, its the water boiling out the turbo cooling pocket and entering the expansion tank as vapour.

Simon

 

Thanks

 

as said, water boiling. so you cool the car down before you turn it off?
have you checked the quality of the coolant, ie has it got enough antifreeze in it, not just water.