About the car model it's E200 92.

About the brakes, yes some times when I'm driving I hear the hissing sound on the brakes and when I press brakes a little bit the sound disappears.

But Whenever I press brakes I hear hissing, espcailly if I'm on a high speed or declining ground.

The sound started when I have changed the rear brakes and the rear brake drums.

About the pedal, I think it's the same nothing changed.