A kinetic formalism of sideband excitation at the multiples of bounce and cyclotron frequencies of electrons trapped in the ponderomotive potential well and a guide field is developed. A positive (negative) slope of the distribution function with parallel energy is necessary for the excitation of upper (lower) sidebands of the bounce frequency. The cyclotron harmonic sideband excitation requires large perpendicular energy; the latter, however, tends to lower the growth rate of bounce harmonic sidebands. In either case the growth rate falls off rapidly with the harmonic number.