Hard to really answer this question without much more detail about your workflow such as camera settings, lens, lighting, codec etc. Generally speaking- apparent grain in any sort of footage is due to one or more of the following possible reasons: underexposure, excessive gain or simply a highly compressed camera codec that doesn’t create a pristine signal. 4K is of course not specifically more or less susceptible to this than 1080p or SD would be. It’s always going to be garbage in garbage out no matter the size of the frame- no offense meant.
Noah
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