Nuclear magnetic spin-lattice relaxation dispersion of nematic 4-pentyl-4'-cyanobiphenyl was investigated at two different temperatures in the presence and absence of sonication. Results were analyzed in terms of the coupling between acoustic waves and nematic order director fluctuations (ODF). Our study suggests that the sonic field induces a clear effect on the ODF spectrum, and that the sonication energy is dissipated among all order fluctuation modes. The proposed physical interpretation is based on a sound induced enhancement of ODF modes. (C) 2002 Elsevier Science B.V. All rights reserved.