hissing noise from ?engine.like gas leak.noise reduced when apply brake

Really many thanks .is this a serious problem...?does it cost a lot to repair ,??do I need bring to audi service centre as I am worry it may cost a lot ....do you repair .....,thank you

I've seen vacuum repairs on Audi's run from as little as $50 to as much as $700. A diagnosis would be necessary to determine the exact nature of your problem. You do not have to go to the dealer for repair - any qualified shop can take care of it - and yes, we can take care of it, too - if that is your question. We're only 15-20 minutes from you.

THANK YOU FOR YOUR HELP.MUCH APPRECIATED.