Noise is different and treated differently.
Only describe the causes of small grains (no stains!).

1. Noise directly from the light. Often, on the border of light and shadow. Particularly strong from Vraylight if there is an object. The closer the object is to VrayLight, the more noise. Increase subdivs of Light or AA settings (preferably find averages for both, not only raising a one parameter)

2. The noise in the materials (and reflect refract glossiness). It depends on the settings of glossiness subdivs in material. Treated with settings of material and AA. Again, it is desirable to gradually raise both. If speed is important of course. If not, you can use DMC AA and increase global multiplier and noise threshold.

3. Noise from highlight glossiness. And often it is not important, use you this option in the material or not. Just when it is used appears more noise. So, the noise treated with rising subdivs but only at VrayLight (NOT IN MATERIAL!) And the AA settings. Naturally you must raise subdivs in that Light from which is the noise.
(c) Saluto