If you want no grain, shut off any thing that boosts or gains the overall brightness.
I wouldn't recommend auto-aperture, but you have to be experienced to know when to use which aperture, so you don't over- or underexpose the image (that's where the grain comes from).
Are you shooting documentary or scenary?
If scenary, I'd say rent a control monitor to check the image before shooting or run some test in different light situation to see which aperture gets you the best result.
If there is a minimal grain left, you can degrain it a bit in After Effects with the degrainer from Sapphire.