Lucky for you, renowned Danish photographer Thorsten von Overgaard posted a video on his YouTube channel where he discusses those topics. This is a great resource for anyone who has been wondering what causes sensor noise and why it varies so greatly across cameras and camera systems.
Overgaard starts his video talking about light sensitivity, which is the key piece to any photography noise discussion. Light sensitivity is what causes film to have more or less grain and sensors to have more or less noise — what it really boils down to is the more sensitivity you want/need, the more grain/noise will be produced.
A great analogy that is used in the video talks about skin color and how some people can get sunburned quickly within a short time of being exposed to direct sunlight, while others with denser light sensitivity can be outside for long stretches of time without running into any issues. This more or less equates over to camera film and sensors as well, with some being more sensitive to light than others, just rather than a sunburn being the result, grain/noise is the result.
Make sure and watch the video as Overgaard makes some great points about what produces sensor noise, how you can avoid it as a photographer and ways that you can use it to your advantage in your photography. These are invaluable tidbits for any photographer struggling with these issues.
