Sound is one thing but also think of the dust, especially if you’re planning to machine pcb at your home. That’s not good stuff.

But speaking of sound, some of it comes from the spindle. The faster it turns, the more noise it makes (usually). I was using a dremel as my spindle some time ago and it was veery noisy. Then I tried another machine that had a bigger spindle, that one was much quieter.

Then there’s the sound of the material being processed. The cutting bit hits the material at spindle_speed*flute_count Hz. This also creates hell of a vibration.

So you need to do two things: dampen the vibrations, and block the radiated noise. Plus you want to make sure you have some sort of dust control.