318ti M44 strange sucking noise

[zerouali]

Hey, I've got a Euro 318ti M44 engine, when I switch the engine off i get a wierd sucking, whooshing noise coming from somewhere round the upper manifold. My mechanic thinks it's to do with the brake booster hose so taking it in next week to get it checked, just wondering if you've heard this or have any ideas that might help him track it down.

Cheers.