Just fitted a concealed door closer to my newly-created internal kitchen.
Used Screwfix quote 12108, and fitting was very easy.

Problem is: it makes a hell of a noise when door closes/opens. The door is a
30 min fire door (pretty heavy one).

Tried to re-adjust height (noticed that it was 1 milimiter out of line -
now perfectly aligned), but it didn't make any difference. Also tried WD40.

Any idea what can cure this?