After reviewing the role Quasi-Normal Modes (QNMs) play in the Gravitational Wave (GW) signals emitted in the ring-down phase of Black-Hole (BH) mergers, we present a novel efficient approach to compute QNMs of BHs, D-branes and fuzz-balls, based on quantum Seiberg-Witten (SW) curves for N=2 supersymmetric Yang-Mills (SYM) theories. We find remarkable agreement with numerical results obtained by means of Leaver's method of continuous fractions and with `semi-classical' results obtained in the eikonal approximation, based on geodetic motion. Finally we discuss the extension to D3-branes and their bound states of Couch-Torrence (CT) conformal inversions, that exchange horizon and infinity, and show that they keep the photon-sphere (or photon-halo) fixed.