Question

why are metals sonorous?

Answer 1

electron bonding in metals is highly delocalized, due to their very low electronegativity. This means that when struck, the electron cloud moves extremely easily producing the kinetic energy required to produce sound

Answer 2

sonorous meaning capable of producing sound
metallic bond is delocalised due to low electronegativity thatenergy cloud move easily and a little energy is dissipated so the metals produce 
 sound
 Electron bonding in metals is highly delocalized, due to their very low electronegativity. This means that when struck, the electron cloud moves extremely easily - there is very little energy dissipated. This allows the incoming kinetic energy to be easily propagated as a form of disequilibrium - a wave. 

Now, it should be noted that this is not in all metals - it is in sheet metals, and they have to be of relatively low density. High-density metals will not as easily propagate the kinetic energy, due to additional atomic collisions damping the effect.