Whistleing brakes on 2002 Volvo V70 XC

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.

by in Lititz, PA on February 28, 2011
1 answer
ANSWER by , February 28, 2011
brake booster could be leaking