Is it, in fact, resonance? Most probably it is cavitation and not resonance as resonance would most likely cause the prop to shatter into little tiny pieces. Cavitation is not necessarily destructive, but results in loss of efficiency of the prop as the air flow over the prop's airfoil becomes turbulent. Resonance occurs when the vibration frequency of the prop is harmonically the same as the wavelength of the prop and will eventually cause catastrophic failure of the prop.

doubledee