There are a lot good things you can do for your desktop PC: Give it an SSD or a bit more memory, clean up your desktop or install cloud backup for your dearest files. None of which need to be terribly time consuming or expensive.
A simple vacuum cleaning is even better. Turn off the PC, open up the case and clean the filters in front of all the fans. Do the same for the heat sinks on the CPU and the video card, as well as the power supply. Less than 5 minutes work and suddenly it is much more pleasant to sit alongside the machine, because with better airflow through the case comes slower running fans and that means less noise.
I recently cleaned a PC at a relative’s house. It had not been cleaned since 2007 and it sounded like a high-power vacuum cleaner. When I was done, they couldn’t hear it was turned on (the PC got an SSD at the same time and is now ready for many more years of service – no wonder new PCs aren’t selling).