We study mechanical energy 1ocalization,which has been experimentally observed by Job [Phys.Rev.E 80 (2009)025602(R)],using computer simulations and the binary-collision approximation.We find interactions of a solitary wave with a light intruder exciting two kinds of localized modes.One is visible in the tail of the incident impulse,and the other is observed when the defect is loaded by the solitary wave.The frequency of localized oscillations is analytically obtained and is in excellent agreement with the numerical results.