Sharan - Starnge air hissing from driver's footwell

[di4charles]

I own a late 2001 VW Sharan (New Shape). Whenever I release the brake pedal I'm left with an air-like hissing noise eminating from the driver's footwell. I can make it go away if I give the gentlest tap on the brake pedal.
I have had my brakes checked by a mechanic who can find nothing wrong (the noise never appears when he is around)! Indeed the car has just passed its MOT.
Any thoughts? Some unimportant rubber boot or gaiter perhaps?

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A month later and things have moved on a bit. The air hissing noise is now constant and louder from the drivers footwell, except when I apply the brakes and it goes away. A mere tap on the brake pedal and I can make the noise go away until the next time I use the brakes. Is there a part with a diaphram that needs changing and if so, how do I access it?

Please, somebody answer. My Sharan has driven 320k miles.

[zorgman]

can be vacuem suck noise from the servo or noise from ecu pipe that lurks near the brake pedal or last thought a pipe going to heater system as that uses vac for flaps. its a case of getting your head in that area take the plastics off bottom of dash for better access

[di4charles]

Thanks for your reply. It turned out to be a leaking brake servo that required replacing.