Hi newbi here.

I have an 08 A3 1.9Tdi and when I'm driving I can here a hiss or air flow sound from the right side air vent dash area. When I press the break pedal the noise reduces and pressing the brakes fully on stops the noise.  I'm thinking it has something to do with the vacuum for the servo, would this be a good shout? Also how do I access the servo to check?

One more question, in the centre arm rest there looks to be an electrical connection of some kind, what was this for? 

Thanks 😊 

A vacuum leak sounds a reasonable diagnosis, but I am puzzled that you hear it from a dashboard air vent. Have you listened under the bonnet?

The engine is too loud when under the bonnet to here anything. 

If you can't trace the leak by listening I suggest you locate the vacuum hose under the bonnet and follow it to the vacuum pump or manifold at one end and the servo at the other. Check for loose connections, splits, etc.