Engine noise at startup

[serch_dci]

Hello to everybody here. I'm a new CLK230K owner over here trying to get the beast back in shape.

I'm a little annoyed by the sound my engine does at cold starts, here is the video:

Not bout the chain tensioner getting the pressure for 1-2 seconds, which i think it's normal for this engine, but the sound similar to a pneumatic valve opening and closing. I think it comes from the black square at the left of the red head cover (IMAGE).

Looking for diagrams couldn't find more than (THIS). I think it's the piece which connects pipes 20 and 35 but couldn't find info or the exact name of the part. any help would be greatly appreciated.

Thanks in advance.