  We report a 139La NMR investigation of low-doped insulating manganite samples
(LaMnO(3+y) and La(1-x)Ca(x)MnO(3+y)) as a function of temperature. A volume
fraction with fast nuclear relaxations was revealed by the inhomogeneous loss
of the NMR signal over a broad temperature interval. Comparison with muSR data
demonstrates that the wipe out of the 139La signal is mainly due to slowly
fluctuating electric field gradients. This provides strong evidence for the
slow diffusion of lattice excitations, identified with Jahn-Teller small
polarons.
