Hissing sound from Exige S2

never noticed this before but theres a hissing sound when i switch off, then a few seconds later a ‘click’. Sounds like its coming from the airbox sort of area.

Being a total auto-condriact i also noticed the engine moves around a lot as I’m driving. Am I going mad?

Do you have an induction kit? They hiss when you turn the engine off. Mine always does when I turn it on as well, sounds like DarthVader is living in my sidepod