  We study linear perturbations of classically stable Q-balls in theories
admitting analytic solutions. Although the corresponding boundary value problem
is non-Hermitian, the analysis of perturbations can also be performed
analytically in certain regimes. We show that in theories with the flat
potential, large Q-balls possess soft excitations. We also find a specific
vibrational mode for Q-balls with a near-critical charge, where the
perturbation theory for excitations can be developed. Comparing with the
results on stability of Q-balls provides additional checks of our analysis.
