  We study fluctuations around equilibrium in a class of strongly interacting
non-conformal plasmas using holographic techniques. In particular we calculate
the quasi-normal mode spectrum of black hole backgrounds that approach to
Chamblin-Reall plasmas in the IR. In a specific limit, related to the exact
linear-dilaton background in string theory, we observe that the plasma
approaches criticality and we obtain the quasi-normal spectrum analytically. We
regulate the critical limit by gluing the IR geometry that corresponds to the
non-conformal plasma to a part of AdS space-time in the UV. Near criticality,
we find two sets of quasi-normal modes, related to the IR and UV parts of the
geometry. In the critical limit, the quasi-normal modes accumulate to form a
branch cut in the correlators of the energy-momentum tensor on the real axis of
the complex frequency plane.
