  We study phonon modes associated with magnetic vortex lattices of finite
isospin chiral perturbation theory near the upper critical point by introducing
quasimomentum fluctuations to the lattice and calculate dispersion relations
associated with the optical and acoustic modes. We find that one of the
acoustic modes is massless and that its energy for small transverse
quasimomentum is quartic (due the presence of an isospin chemical potential),
which is significantly softer than the "supersoft" (quadratic) massless mode of
the Abelian Higgs Model (AHM). Due to the presence of derivative interactions,
which is absent in the AHM, the speed of the longitudinal mode depends on both
the isospin chemical potential and the external magnetic field. Our results
suggest that the standard assumption of an ordered lattice in finite isospin
QCD should be revisited and the existence of a disordered spaghetti phase of a
vortex liquid or gas, should be considered.
