Are the temps looking OK? Could it be a poor connection between CPU and heatsink - more thermal paste or a new thermal pad needed? If it's second hand the machine may have had a life in an enclosed/warm space. Have you tried blowing any dust out?
The reason I ask is that I can't even hear the HP i7 I have when it's in operation...
Could try your luck with a replacement: https://www.amazon.com.au/QUETTERLEE-Replacement-Cooling-Elitedesk-L19561-001/dp/B08ZC51KRR
You could also try having a larger fan blow over it for quieter active cooling or see if you can get some passive cooling with heatsinks or sitting it on some other condutive mass.
I got most of them from here: https://www.thingiverse.com/thing:3337383
I also picked up this rack rail set to mount the prints to: https://www.amazon.com/dp/B072B9H3FC
Once everything was screwed in it became super stable.