The magnetic-field-dependent change in the sound velocity was measured in the mixed state of V-42 at.% Ti at T=4.14K, using shear and longitudinal waves with frequencies 10-30 MHz, in magnetic fields of up to 90 kG. For H<H_c2, the results are compared with phenomenological models in which the flux-flow resistivity is used as an effective resistivity in the Alpher-Rubin theory. Good agreement between theory and experiment is observed for longitudinal waves. However, for shear waves, these models overestimate the observed mixed state velocity changes.