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

3 answers
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.
POSS BRAKE BOOSTER IS LEAKING
Sound like other are right , we do a fair bit of them