I have a 58 reg A3 1.9 TDIe and a hissing noise has started coming from the foot well as I rev or drive along. If I put my foot on the brake it seems to stop. I have read a few articles which say it maybe the brake servo which is bust. Half the articles have a noise which stops when the brake pedal is pressed and some it starts and im not sure which way around is of concern. I have just taken it to a garage and they say the vacuum is all fine and that perhaps as its when I accelerate perhaps there is a noisy bleed valve inside there so when revving the pressure doesn't get to high and cause over aggressive breaking. Can anyhow help this is a bit of a concern as I do many miles and don't want the brakes to fail if there is a fault but also don't want to spend hundreds on something normal. Thanks in advance mike