Tunnel diode I-V curve noise
The Tektronix 571 Curve Tracer used in the photograph is an early instrument whose Operators Manual is here http://w140.com/tek_571.pdf. The manual does not mention tunnel diodes but states on p.2-9 that images of transistor behaviour at very low voltages and current may be noisy. It also acknowledges on p.3-18 a problem with devices that oscillate. It is not capable of reducing noise by integrating repeated measurements. I speculate that dwelling at any point on the negative resistance region for the time required to measure each sample creates a high gain amplifier for ambient noise, or even an oscillation at a frequency far higher than the ADC is able to "see"