I always thought that the noise in the computer is created exclusively by fans working inside to drive air. Oh how wrong I was! After all, the main part of the noise is created by the body of the computer itself. All vibration from all the working parts of the computer, such as a hard drive, fans or cooler, is transmitted to the case.
And what is most interesting is that the vibration from the case is pretty well transmitted to surrounding objects, in particular to the stand on which the computer is standing. I will offer you one simple step to understand - it will take five minutes to make your PC a little quieter!
For this, it is necessary to put vibration-absorbing material between the PC and what it stands on. The material may be different, but the softer and thicker the better. In the top of these materials will be a piece of foam.
Here is my pc. It makes a decent noise.
After the soft fabric backing, the difference is quite noticeable! In particular, low-frequency noise has disappeared.
I advise you what to do.