Does any other setting besides ISO affect noise?

I understand the darker it is on a entry level body like the 60D the more noise will occur in general. So of course smaller apertures and whatnot after say 5PM make the shot too grainy. I was just wondering why my shots are so ridiculously grainy though. I shoot ISO's 320, 640 or 1250, use Cinestyle picture style, and 1/50th for 24fps. My meter barely touches -1 so I know my image is too dark, which I always brighten in Premiere. The shots look lovely but by the time theyre on the computer the noise is just too much. I've seen many people on Youtube shooting with the 60D without L lenses and they still get much less noise than I do. What am I doing wrong

Have you tried playing with any noise reduction filters in post?

Under exposure will generate noise. Noise has nothing to do with the quality of the lens but a great deal to do with aperture. If someone had faster glass than you they are less likely to get noise.