We study the inflationary model with a spectator scalar field 𝜒 coupled to both the inflaton and Ricci scalar. The interaction between the 𝜒 field and the gravity, denoted by 𝜉⁢𝑅⁢𝜒2, can trigger the tachyonic instability of certain modes of the 𝜒 field. As a result, the 𝜒-field perturbations are amplified and serve as a gravitational wave (GW) source. When considering the backreaction of the 𝜒 field, an upper bound on the coupling parameter 𝜉 must be imposed to ensure that inflation does not end prematurely. In this case, we find that the inflaton’s evolution experiences a sudden slowdown due to the production of 𝜒 particles, resulting in a unique oscillating structure in the power spectrum of curvature perturbations at specific scales. Moreover, the GW signal induced by the 𝜒 field is more significant than primordial GWs at around its peak scale, leading to a noticeable bump in the overall energy spectrum of GWs. It is worth noting that this bump predicted in the slow-roll inflationary scenario is unlikely to be detected by LISA and Taiji, but there is a slim chance it might approach the detection limits of GW experiments like BBO and SKA if we devise distinctive inflatonary potentials.