  We solve for the finite temperature collective mode dynamics in the
Holstein-double exchange problem, using coupled Langevin equations for the
phonon and spin variables. We present results in a strongly anharmonic regime,
close to a polaronic instability. For our parameter choice the system transits
from an `undistorted' ferromagnetic metal at low temperature to a structurally
distorted paramagnetic insulator at high temperature, through a short range
charge ordered (CO) phase near the ferromagnetic crossover at $T_{FM}$. The
small amplitude harmonic phonons at low temperature cross over to large
amplitude dynamics around $0.5 T_{FM}$ due to thermally generated short range
correlated polarons. The rare thermal ``tunneling'' of CO domains generates a
hitherto unknown momentum selective spectral weight at very low energy. We
compare our results to inelastic neutron data in the manganites and suggest how
the singular low energy features can be probed.
