<human>:  How does the author explain the difference between the noise in a system and the noise in a signal?
<bot>: The author explains the difference between the two in Chapter 2 of the book. The author uses the example of a car engine. When the car is stationary, the engine makes a constant noise. However, when the car is moving, the engine makes a signal. The noise is a property of the engine itself, while the signal is a property of the engine when it is in motion.