I need a noise effect in my game. What is the best way to do that?

Yea, you want to use a shader as an image effect. There's actually a noise example in the Standard Asset for image effects. Go check that one out, it should give you a good starting point. You probably just want to make the noise amount a tweakable variable and animate it during runtime. Additionally you can add distortion effects etc via the same method, but it's all shader domain, so a good chance to get into shader programming or at least look at the examples and modify them to your needs.