The sound that you hear over Oslo when the troll is near is the sound of flight alert or 'Flyalarmen'. It is mostly used to make people known about an coming threat, like a terror attack, a gas leak or an earthquake. This sound is tested twice a year. The last time it was played for real was in Oslo in 2011. It's actually the exact same as the Swedish VMA. (Important message for the public).
Some of the soldier's screams you hear after Tidemann calls Captain Holm on his mobile are sound effects from Command & Conquer: Der Tiberiumkonflikt (1995).
WILHELM SCREAM at 47:13 (After the artillery attack, when the troll kicks the military vehicle into the trees).
Principal photography began in August 2021 and wrapped in November, with location shooting taking place in Askim, Dovre, Indre Østfold, Lom, Øyer, Rena, and Ulsteinvik.
The music in the trailer is Edvard Grieg's In the Hall of the Mountain King.