Your PC will also show signs of struggle, meaning fans will run faster, producing more noise as your PC overheats. For conclusive proof that your CPU is throttling, open any CPU monitoring program like OpenHardwareMonitor or HWiNFO while putting your CPU under stress with either a CPU-intensive...
But the fans will spin up like this when there is a fatal error with your system, you need to reset your bios options to default and run HWinfo logging when you are playing games or doing usual stuff to see if it picks anything up, what is your CP...