A JWST/NIRSpec archival study of 87 massive quenched galaxies at z~1.5-4.5 detected the high-ionization [NeV] λ3427 line in just six systems, providing unambiguous evidence of ongoing supermassive black hole accretion long after star formation has ceased. With an ionization potential of 97 eV, [NeV] cleanly traces quasar-level activity (L_bol ~10^45-46 erg s^-1) without contamination from residual star formation; four of the six also show broad Hα (FWHM ≳4000 km s^-1), yielding BH masses of 10^8.5-9.5 M_⊙ that sit on local scaling relations. The strongest [NeV] emitters reside in the youngest post-starburst galaxies (D_n4000 ≲1.3), while older quenched systems are devoid of such signatures, a pattern independently recovered in the theoretical models cited by the authors. This implies duty cycles of 100-200 Myr during which radiatively efficient accretion persists hundreds of Myr after the main quenching epoch, with BH accretion rates sometimes rivaling or exceeding residual SFRs. The work is a preprint (arXiv:2605.30424) and therefore not yet peer-reviewed; the sample of six detections is modest and drawn from archival spectra, limiting statistical power. Related analyses of local post-starburst AGN (e.g., Pawlik et al. 2018, MNRAS) and cosmological simulations of AGN feedback (e.g., Hirschmann et al. 2023, MNRAS) suggest that such late-phase accretion may inject sufficient energy to maintain quiescence, an under-reported regulatory step that current cosmic feedback prescriptions often omit or under-time.