Strange brake noise

[Phrog]

My 2001 XC with ~35k miles has a new strange noise. (I haven't
actually heard it, this is all based on reports from someone who is
using the car). When releasing the brakes, there is a rushing
air / whooshing sound; described like "a bike tire leaking".
This only happens when she takes her foot _off_ the brakes, not
when she applies them. And it happens only after driving for ~15 minutes.

Anyone? Anyone? Bueller?

[tgrumaj]

The closest I've come to that sound was when I had a pair of Nike's that had and air cushion sole and there was a nail (or something sharp) that must have punctured the air bladder. Whenever I took a step it sounded like air rushing coming out of an air pump or a tire. There was no noise when I stepped down but then a release of air/air being sucked in sound when I picked my foot up and air rushed back in!! Maybe you should ask the driver what type of shoe they are wearing!?

[KnowItAll]

Phrog,

Try depressing brake pedal while in PARK,but the motor MUST be running.
Step a couple of times.The air noise (sounds like a balloon when letting the air out to create a high pitched noise). That noise you hear is the brake booster ( large black,round object on firewall in motor compartment).
When the brake booster goes bad ,vaccume bleeds out of the back into the cabin. That's why its audible to you, the brake pedal is connected to it.
You will not lose your brakes,but as it gets worse the pedal may get stiff.
Time to take it in for repair.Sadly,It will require replacement for correction.

[Phrog]

Yes it was the brake booster, and was replaced under warranty.
Know-it-all, you are living up to your moniker.

[KnowItAll]

Phrog,

Glad to be a help......Drive safe! ;)