Since months, my laptopt was getting hot and spinning its fans.
The usual explanations kicked in: "It's old. It's a Macbool with an intel chip, known to overheat. Must be the new software running on old hardware."
Today I've finally thought for 5s to come up with the idea the the fans might be full of dust after 6 years.
Opened it up (still had a stupid pentalobe screwdriver somewhere), cleaned it out and now it's good as new :)