I have a 2002 Jetta. After I turn the engine off there is a noise coming from the front of the car. It sounds kinda like hissing but not quite. I thought at first it was a fan running to cool it off but don't see any fan. It does this for about 10-15 mins. after turning it off. I have asked many people, mechanics and nobody knows. I could go to the VW dealership but it's about 1 1/2 hours away. What could it be?