I have never had any kind of brake problem, so always assumed it was normal, but no one has ever been able to tell me WHY...

When I am not braking, my brake pedal "breathes." Some would probably call it a hiss... but it is lower pitched than that. More of an exhale. Air escaping from something in the mechanism. If i put my foot on the pedal, noise stops. Assuming something about the hydrolic/strut return mechanism... Does everyone experience this?

 

vacuum leak