This work is based on the experimental evidence from ultrasonic absorption spectra, measured between about 100 kHz and 5 GHz for some series of liquid mixtures with water as a constituent. Since none of the existing models of noncritical concentration fluctuations appropriately applies for the shape of the existing set of spectra, a comprehensive theoretical model has been derived which includes the favorable characteristics of previous theories. In this model, fluctuations in concentration are assumed to equalize not only by diffusion but, in parallel, also by a specific rate process In addition, allowance is made for spatial correlations in the concentration fluctuations. Discussion of the measured ultrasonic spectra in terms of the comprehensive model evidences the effect from the hydrophobic properties of:the nonaqueous constituent of the mixtures upon the microheterogeneous structure of the liquid.