Vacuum loss?
 

Hello all.
I am the owner of a 1992 190e 2.3 8v. I have read that the beam height adjustment of our cars is controlled by vacuum of the engine's inlet manifold.
In my car, when it is in one the extreme positions (I don't remember which), it sound a little hiss. It worries me that could be a slight vacuum loss that could affect the performance of the engine. Can this have any influence or it is normal?

Thanks!