sounds like air when I step on brakes on 2001 Volvo V70 XC

my question was when I get in the car and back out of the driveway when I step on the brakes it sounds like air coming out

by in Naugatuck, CT on August 19, 2013
3 answers
ANSWER by on August 19, 2013
POSS BRAKE BOOSTER IS LEAKING
ANSWER by on August 19, 2013
THE AIR LEAK TYPE NOISE WHEN STEPPING ON THE BRAKE PEDAL IS DUE TO THE BRAKE BOOSTER HAVING AN INTERNAL DIAPHRAGM VACUME LEAK. CAN BE FELT WHEN STEPING ON THE BRAKE PEDAL OR RELEASING THE BRAKE PEDAL,OR THE AIR LEAK CAN BE CONSTANT. BRAKE BOOSTER NEEDS TO BE REPLACED.
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ANSWER by on November 05, 2013
Sound like other are right , we do a fair bit of them
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I have a hissing sound and whistle from (a braking) component. Reason, when I step (press) on the brake pedal the noises stop. Any clue as to what this is. It sounds like an air leak.
it happens everytime I get in the car and back out to the main rd but after driving for about 5 mins the sound goes away