The Supra-Arcade Downflows (SADs) in the solar corona develop over coronal arcades and propagate toward the sun for a short period. We investigate SADs for possible occurrences of Kelvin-Helmholtz Instability and emission of Magnetosonic waves. We believe the evolution of these two phenomena together may explain the unknown reasons for sudden termination of SADs. The fast and slow magnetosonic waves emitted by the KHI along these boundaries may also contribute to solar coronal heating by way of energy dissipation and wave coupling. In this study, we specifically focus on how the KHI evolution and magnetosonic wave emission are affected by the density depletion in SADs.