Spindle itself isn't too noisy. It's tool's flutes hitting the material makes the majority of noise. Some mills make more some less noise. Strait flute is more noisy than spiral. Cutting the edge rack does influence noise level as well.
However, sometimes steppers make more noise than spindle itself. Unbalanced flycutter can increase noise level, like in case of my pulleys cutting.


Rattling tools on machine bed make lots of terrible noises as well :whistling: