Why do I get stutters in dark corridors in Splinter Cell?

While sneaking through dark corridors, the screen had several obvious stutters that completely destroyed the stealth atmosphere. I tried disabling some environmental lighting effects; although FPS rose by 2, the violent temperature fluctuations remained. I then entered the GamePP Fan Curve Configuration Panel, lowered the fan start threshold to 45℃, and enabled Fast Response mode. RTSS showed frame time converged to 14-18ms, and CPU temperature stabilized at 60-68℃ per AIDA64, with frequencies at 3.1-3.7MHz per CPU-Z.