  We investigate the transition from sub-Poissonian to super-Poissonian values
of the zero-temperature shot noise power of a resonant double barrier of
macroscopic cross-section. This transition occurs for driving voltages which
are sufficiently strong to bring the system near an instability threshold. It
is shown that interactions in combination with the energy dependence of the
tunneling rates dramatically affect the noise level in such a system.
Interaction-induced fluctuations of the band bottom of the well contribute to
the noise and lead to a new energy in the Fano factor. They can enhance the
noise to super-Poissonian values in a voltage range preceding the instability
threshold of the system. At low voltages, interactions may either enhance or
suppress the noise compared to the the non-interacting case.
