  We predict sound anomalies at the doping $\delta_{p}$ where the pseudogap
ends in the normal state of hole-doped cuprates. Our prediction is based on the
two-dimensional compressible Hubbard model using cluster dynamical mean-field
theory. We find sharp anomalies (dips) in the velocity of sound as a function
of doping and interaction. These dips are a signature of supercritical
phenomena, stemming from an electronic transition without symmetry breaking
below the superconducting dome. If experimentally verified, these signatures
may help to solve the fundamental question of the nature of the pseudogap --
pinpointing its origin as due to Mott physics and resulting short-range
correlations.
