Noise in volume

[ghiom3d]

hello, Please, can you explain how to kill this noise in volume renders ?
I'm trying to Up volume sampling, GI or not GI .. but still here when using dome lights or Gi environement lights.

[ghiom3d]

Looks like it's something related to CPU render. If i render with GPU it's noiseless.
But, there is another one issue with GPU, using multiples volume grids make some volume box appearing inside..

[ghiom3d]

Find It ! It's " Use light Cache " in smoke color from the Volumetric options.
With or without GI, event very high light cache seeting or very, this noise is visible and not change.
Unchecking this seeting remove this noise