  We find excitations lower in energy than known phonon modes in underdoped
La$\_{2-x}$Sr$\_x$CuO$\_{4+\delta}$ (x=0.08), with both inelastic X-Ray
scattering (IXS) and inelastic neutron scattering (INS). A non dispersive
excitation at 9 meV is identified and is also seen by INS in
(La,Nd)$\_{2-x}$Sr$\_x$CuO$\_{4+\delta}$, with 40$\%$ Nd substitution. INS also
identifies a still lower energy dispersive mode at low q in the Nd free sample.
These modes are clearly distinct from the longitudinal acoustic phonon and
correspond in energy to the Zone Centre modes measured by optical spectroscopy
and associated with stripe dynamics.
