The radiator makes unbearable noises throu out the night, which drives her insane. We think that this is due to air pockets in the pipes, we can hear crackling and water drops.
The heating system is common to the whole building, and I cant turn off hot water.
How do i open this shit
Was going to say this exact thing, good thing someone else of sound sense has typed the correct answer. Just turn the screw pictured open (counter-clockwise) ever so slightly to let air out (makes hiss) and tighten once water comes out (makes no sound).
Source: Nordic man of the house. I did this a lot until we put in a new heating system with an automatic valve at the main heat reservoir.