Gaming PC randomly freezes?

This issue first appeared a few months back and I'm getting tired of it as it really ruins immersion. It only happens while doing more demanding tasks like gaming, with some games causing more frequent freezes than others. The worst culprits are graphical intensive games, cutscenes, simulation games and when... show more This issue first appeared a few months back and I'm getting tired of it as it really ruins immersion.
It only happens while doing more demanding tasks like gaming, with some games causing more frequent freezes than others. The worst culprits are graphical intensive games, cutscenes, simulation games and when I'm multitasking, like playing a game and watching a video at the same time.

What happens is that everything randomly freezes and I hear a loud buzzing noise coming from the speakers.
I first suspected this might be to due to overheating and the pc somehow locks up for safety reasons, but both my cpu and gpu temps are completely normal.

As you can probably tell my knowledge is limited but I've tried cleaning off dust from the case and every single hardware, reinstalled ram in different slots in case a port was failing, leaved the case open and put a fan next to it to allow more airflow. I've also tried to remove and install new drivers but to no prevail.

The pc was built in 2013 so I have a feeling some hardware is failing but I don't know how to locate the issue. I have read that the most likely culprits could be my psu, cpu, gpu, failing ram or even mobo, but I don't have any spare parts so I have no way of testing it.
I'm getting to the point where I'm considering to take a stab in the dark and start replacing hardware, but I would prefer to spend as least money as possible.

Specs below.
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