This study explores sound alternations in a consonant cluster in which at least one consonant is a sonorant (a son/C cluster, hereafter). In this study, I argue that phonological processes affecting son/C clusters result from low perceptual salience rather than from the Syllable Contact Law as discussed in Vennemann (1988), Clements (1990), Rice & Avery (1991), Baertsch & Davis (2000), among others. That is, as a main factor motivating the alternations in the cluster, I consider contrasts of weak perceptibility triggered by phonetic similarity between two members of a cluster (Kawasaki 1982, Ohala 1992, 1993). Based on the findings from a typological survey in 31 different languages, I show that a speech perception-based account makes a correct prediction regarding the patterning of sonorant/sonorant sequences and that of obstruent/sonorant sequences, while the syllable contact account does not.