Quantitative studies of the correlation between sonochemical activity and acoustical noise spectra have been performed. The width of the second harmonic (fwhm2) of the acoustical signal in the frequency domain shows a sensitive dependence to the presence of small amounts (mM range) of an anionic, surfactant in water. This sensitive dependence is also observed for other characteristics of the cavitation noise spectrum and in the sonochemical production of peroxides and correlates well with the sonoluminescence intensity observed by other researchers. Analysis of the experimental data shows that SDS probably modifies the coalescence phenomena.