Abstract：Astrophysical black hole candidates might be horizonless exotic compact objects. Of particular interest is the plausible fundamental connection with quantum gravity. The puzzle is then why we shall expect Planck scale corrections around the horizon of a macroscopic black hole. Taking asymptotically free quadratic gravity as a possible candidate of UV completion of general relativity, I will show how the would-be horizon can be naturally replaced by a tiny interior with only Planckian deviation for sufficiently dense matter distribution. The new horizonless object may then be the nearly black endpoint of gravitational collapse. Gravitational wave echoes in the post-merger phase of compact binary coalescence provide a great opportunity to probe horizonless exotic compact objects in general. Given the uncertainties associated with the echoes waveform, I will discuss using simple windowing methods to extract a signal from noise. Applying these methods to the LIGO data, tentative signals for echoes are found for multiple LIGO compact binary merger events.