That's normal, it's like crinkling, tinnitus, blood rush, etc. that people hear when using closed back headphones or IEMs and TWS earbuds, and so on. That's part of why some people can't use Etymotics (basically best noise reduction/isolation available, often on sale too) as it makes them too conscious of their breathing, heart beat, etc. and they don't think they can get used to it (the hyperawareness disappears over time).

If you describe it as creaking with the jaw, search up TMJ issues.

Earwax, hearing health, et cetera with Etymotics and other bullet style IEMs: https://www.reddit.com/r/HeadphoneAdvice/comments/10iwqmt/does_insertion_depth_affect_volume/j5ifw7r/ and https://www.reddit.com/r/HeadphoneAdvice/comments/11d8pns/buying_highend_headphones_with_tinitus/ja7u9ii/

To not hear the hum of the PC, you can try getting aftermarket case fans for your computer case and also your GPU and CPU.

I use Noctua NF-A12x25 PWM for basically everything, but that's only because I'm really sensitive to noises. Most people will be fine with the Arctic P12 PWM PST (5 Pack), just be aware of certain RPM ranges with that particular case fan.

FYI, the cooler your room is, the less revving up and down that your computer case fans and GPU/CPU cooler fans will do (especially when under sustained load from high framerate/resolution), so just be aware of the overall ambient temperature.

If you are encountering actual coil whine or buzzing from the GPU/CPU, you can change the coolers and fans for those. If you are hearing buzzing from the hard drive, there's 1TB/etc. NVMe SSDs or the older SATA SSDs for real cheap these days and it looks like they'll keep getting cheaper for the near future, so no need to hear noises from the hard drive, get one of those external hard drive docks/readers/instead if you want to access your excess media.

Open back headphones and solutions to PC noises: https://www.reddit.com/r/HeadphoneAdvice/comments/xpa9zd/pc_noise_with_open_back_headphones/iq2znjn/

Basically search up Noctua fans. Specifically the Noctua NF-A12x25 PWM fans.

These days there's the Thermaltake ToughFan 12, Phanteks T30-120, etc. that are a bit cheaper/better/etc. compared to Noctua. The Arctic P12 PWM PST (5 Pack) is still the best value, just be aware of the annoying resonance range, it's like ~1000RPM.

How to maybe soundproof your room for better noise reduction/isolation: https://www.reddit.com/r/headphones/comments/10epr17/struggling_to_enjoy_my_headphones_in_noisy/j4t4qaw/

If you get (legit, the expensive heavy ones, not the light/cheap/etc. ones) blackout curtains and tape them, it should do some changes. Though actually even using those plastic film thermal insulation kits did nicely as the vacuum seal on the window reduced the sound a lot.

Those thermal insulation kits will help a lot with not needing to run the air conditioner (or heater) all the time, you can keep it on a timer if your AC unit has that option. Just make sure to achieve that good/perfect vacuum seal with the windows when it comes to taping it. There's also those door draft stopper or like foam you put at the bottom of the door, those can actually help quite a bit too with retaining the heat/cold, believe it or not.

Old school earbuds, earphones, et cetera are having a resurgence right now, more info here alongside microphonics, background static, occlusion effect, et cetera: https://www.reddit.com/r/headphones/comments/119tndv/please_explain_inear_to_me/j9o244r/

The above thread link talks about ANC or that noise reduction/isolation.

You might also want to try lessening the clamping force of the headphones, see below.

For comfort with headphones, if you have a big head, ear piercings, glasses, et cetera, basically anything that will interfere with the seal/fit of the earpads, here's more info about headphones and glasses and workarounds it: https://www.reddit.com/r/HeadphoneAdvice/comments/zkjjcu/are_there_any_headsetsphones_that_are/j00kjt2/