Vacuum leak

[oigle]

2003 ML270. Some time back, about 20 seconds after engine shutdown, a whistle occurred which went for maybe 3 seconds. Sounded like from around vacuum booster area. Other times, no issues. Recently, whistle has stopped but I now hear a constant airleak sound from similar area whilst motor is running. Push brake pedal and noise stops. Brakes still work normally.
Can anyone enlighten me as to probable cause? Booster diaphragm failure or hose leak or whatever it might be before I start pulling things apart. Think I need to do something before I maybe lose brake boost.

Ian.

 

[John77]

I have just bought an SLK and I found a similar problem. See https://forums.mercedesclub.org.uk/...queal-from-the-brakes-when-stationary.192651/
On mine, it seems to come from the joint on the pipe. See photos. I haven't investigated further yet, but I think that there may be a seal on the pipe and will need replacing. It happens when the brake pedal is pressed and started to release it.