Ultra-light primordial black holes (PBHs) with masses M
PBH < 5 × 108g
can dominate transiently the energy budget of the Universe and reheat the Universe through their
evaporation taking place before Big Bang Nucleosynthesis. The isocurvature energy density
fluctuations associated to the inhomogeneous distribution of a population of such PBHs can induce
an abundant production of GWs due to second-order gravitational effects. In this work, we discuss
the effect of primordial non-Gaussianity on the clustering properties of PBHs and study the effect
of a clustered PBH population on the spectral shape of the aforementioned induced GW signal. In
particular, focusing on local-type non-Gaussianity we find a double-peaked GW signal with the
amplitude of the low-frequency peak being proportional to the square of the non-Gaussian parameter
τ
NL. Remarkably, depending on the PBH mass M
PBH and the initial abundance
of PBHs at formation time, i.e. ΩPNH,f, this double-peaked GW signal can lie well
within the frequency bands of forthcoming GW detectors, namely LISA, ET, SKA and BBO, hence
rendering this signal falsifiable by GW experiments and promoting it as a novel portal probing the
primordial non-Gaussianity.