  The contribution to the low frequency internal friction and the thermal
conductivity due to optically vibrating edge dislocation dipoles is calculated
within the modified Granato-Lucke string model. The results are compared with
the recent experiments on plastically deformed samples of Al, Ta and Nb at low
temperatures. It is shown that the presence of a reasonable density of
optically vibrating dislocation dipoles provides a good fit to the thermal
conductivity in superconducting samples. At the same time, the internal
friction experiments can not be described within the standard fluttering string
mechanism. We found that the problem can be solved by assuming random forces
acting on the dislocation dipoles. This gives an additional contribution to the
internal friction which describes well the experimental data at low
temperatures while their contribution to the thermal conductivity is found to
be negligible.
