  We revisit graviton production via Bremsstrahlung from the decay of the
inflaton during inflationary reheating. Using two complementary computational
techniques, we first show that such 3-body differential decay rates differ from
previously reported results in the literature. We then compute the stochastic
gravitational wave (GW) background that forms during the period of reheating,
when the inflaton perturbatively decays with the radiative emission of
gravitons. By computing the number of relativistic degrees of freedom in terms
of $\Delta N_\text{eff}$, we constrain the resulting GW energy density from BBN
and CMB. Finally, we project current and future GW detector sensitivities in
probing such a stochastic GW background, which typically peaks in the GHz to
THz ballpark, opening up the opportunity to be detected with microwave cavities
and space-based GW detectors.
