A phenomenological analysis is carried out to investigate the propagation of sound wave in the positive column of a glow discharge plasma. Specifically, the effect of local energy transfer from the discharge into the gas is studied. The analysis shows that the density fluctuations cause variations in the energy transfer rate. This effect is found to be a function of the plasma parameters and acoustic wave frequency thus leading to acoustic dispersion. The conclusion confirms earlier mathematical treatment of the problem [Kolosov et al., AIAA Paper No. 99-4882, 1999] and provides a physical explanation of the phenomenon.