Here is a pic that should help explain what I mean -



If I move the vac pipe up & down the connection that sticks out of the vac pump also moves up and down.

I am not 100% sure of its designed to do this or the connection is broken, as this is were I can hear the hissing.

I hope it not broken as a new one around £300.

My mate has got a A4, so I checked his, but his is a newer version and has a different engine code and vac pump.

Hope someone can help, as it can be a bit scary when you press the brake pedal and its rock solid and the car in front has stopped.