I've shot film and video for 30 years, but am new to the Canon Mark lll. Today, I'm returning my second camera in two weeks due to unacceptable noise and faint vertical stripes in underexposed areas. ISOs in multiples of 320 minimize but don't eliminate the problem. Flat picture profiles, which I prefer for grading, make the issue worse.
The problem is very obvious even with video displayed on a broadcast monitor direct out of the HDMI port. It is more subtle on the attached still grab, but still apparent in the wall upper left. When panning, it's almost as if I were shooting through something vertical very close to the lens. BTW, I've tried several lenses as well as older and current Canon firmware. Haven't loaded Magic Lantern yet. Insights would be appreciated. Is this just how it is supposed to look?
As Meatball_Sub wrote, that amount of noise is absolutely normal when you underexpose a dark area, expecially with hi ISO and flat picture profiles. You can reduce a bit this problem using the Magic Lantern ISO settings and the maximum in-camera hi ISO noise reduction, but you won't get rid of it. As far as I know, color grading is the only way to achieve a "dark look" without a lot of video noise.