Every amplifier regardless its technology or topology contains noise sources. Some topologies are better than others. Once you have made the design, the amplifier has a minimum noise figure, most simulators are able to perform this measurement (ADS, MWO, Ansoft designer, ...). The minimum noise figure is obtained when the source impedance equals a certain value. Then you design you input matching network so that the actual source impedance is transformed into this optimum value. That's more or less the global story.