"Aspects of Noise Reduction in RAW Data"
And then there's thermal noise. While most modern DSLR's can control that magenta or blue amplifier glows, noise still increases in warm weather. It's always there. The question is, "How much can you tolerate or control?"
If you can't read enough about digital noise, check out Emil Martinec's great article "Aspects of Noise Reduction in RAW Data". This is some pretty technical stuff. But it makes great reading if you have the time to read through it slowly.