  Fluctuations pose fundamental limitations in making sensitive measurements,
yet at the same time, noise unravels properties that are inaccessible at the
level of the averaged signal. In electronic devices, shot noise arises from the
discrete nature of charge carriers and it increases linearly with the applied
voltage according to the celebrated Schottky formula. Nonetheless, measurements
of shot noise in atomic-scale junctions at high voltage reveal significant
nonlinear (anomalous) behavior, which varies from sample to sample, and has no
specific trend. Here, we provide a viable, unifying explanation for these
diverse observations based on the theory of quantum coherent transport. Our
formula for the anomalous shot noise relies on---and allows us to resolve---two
key characteristics of a conducting junction: The structure of the transmission
function at the vicinity of the Fermi energy and the asymmetry of the bias
voltage drop at the contacts. We tested our theory on high voltage shot noise
measurements on Au atomic scale junctions and demonstrated a quantitative
agreement, recovering both the enhancement and suppression of shot noise as
observed in different junctions. The good theory-experiment correspondence
supports our modelling and emphasizes that the asymmetry of the bias drop on
the contacts is a key factor in nanoscale electronic transport, which may
substantially impact electronic signals even in incomplex structures.
