How would this circuit work as a white noise generator?
The left-hand transistor is being used as a diode - not only that, as a reverse-biased diode operated in breakdown. This process is notably noisy, and the 100 nF capacitor blocks the DC level from the subsequent amplification. A lot of NPN signal transistors have base-emitter breakdown voltage in the range of 6 to 9 volts, so a supply voltage of at least 12 volts is a good idea for this approach to work, although with proper transistor selection you might get away with a 9 volt battery. Note that, for instance, a 2N3904 has a minimum breakdown voltage of 6 volts, but that is a minimum value and cannot be relied on.