vaccum noise

[jrgoodman]

New to the board, 3 time BMW owner. I just bought a 2002 325I.There is a rubber cover behind the brake pedal that whistles when it is not engaged, gets louder when partially engaged and goes quiet when fully engaged. Is there a vacuum related to the brake pedal?

thanks
JR - florida [???1]

 

[Kirby]

The big round part below? This is the vacuum booster. It "multiplies" the pedal pressure by using vacuum from the engine. If the rubber diaphragm fails, it could make a hissing/whistling sound. Never had it happen on a BMW, but I did have it happen after about 60K miles on my GMC Suburban. I replaced the booster and it was fixed.