Loud cracking noise sometimes

Hey guys, long time lurker here but never really signed up as i've usually found a solution to everything by searching, but i have a weird predicament i was hoping some more tech savvy people could help me with

So when i'm using my computer, i usually have no problems, the rig runs great and everything is running smoothly, however i get an odd issue when i game sometimes.

In my opinion, frmo the sound of it it sounds like my case expanding due to the increase of airflow and heat, but when i'm in a gaming session, randomly (mostly once a day but sometimes not in the day) i will hear a cracking sort of noise, kind of like pushing in plastic into a clip sort of noise, usually when i'm playing a game where its like medium high to high load.

I've tested all the compartments, and i've ran really vigorous benchmarks to try and emulate the noise but it never does, only say, 50 minutes into a gaming session will it do this? that is if it even does, and my temps go from 30 to about 50-60 max on load for CPU and GPU is always cool, ram too.

I've looked inside, no capacitors ever blow, nothing ever looks bad, the only thing i can think of is potentially a PSU fault or my old Hard Drive giving in the ghost, but it does it on games where i'm even running my SSD.

Is it potentially the change of heat on my rig causing the case to expand ever so slightly or is it something faulty, its happened for give or take 2-3 months now, if anything id of expected something more bad to happen now than ever but nothing ever seems faulty.

Any help would be awesome! Cheers guys And i hope i can help people out here aswell in the future.

(Sorry if i have this in the wrong section or anything, lemme know and i'll move it)

Specs of the PC?