  Current fluctuations generated by tunnel junctions are known to be
non-Gaussian. However, this property is lost when fluctuations are measured at
high frequency and limited bandwidth. We show that the quadratures of the
electric field generated by a tunnel junction at frequency $f$ displays third
order correlations, i.e. skewness, when the junction is electrically driven at
$3f$, revealing the Poisonnian statistic of charge transfer by the barrier even
at short time-scales. In addition to this intrinsic contribution from the
junction, we observe extra correlations induced by the environmental noise at
frequency $f$ as well as a feedback effects coming from the environmental
impedance not only at frequency $f$ but also at some multiples of $f$.
