The sounds from certain types of gongs show a frequency shift, up or down, as the vibration decays. In order to understand this nonlinear behavior, we have studied the vibrations of a variety of fiat and curved plates under v•trying amounts of radial tension or compression. Flat plates show a nonlinearity of a hardening type {falling frequency), whereas most curved plates show softening behavior (rising frequency). The degree of the nonlinearity appears to be sufficient to explain the observed frequency shift in the gongs studied.