The effect of background noise on speech perception is a multifaceted phenomenon. Psycholinguists often attribute the reduced intelligibility in noise to energetic masking: weak elements of the speech signal are not audible anymore and cannot contribute to recognition. Yet, noise also introduces random fluctuations that disrupt perception in less obvious ways. Using a reverse correlation approach, we examined how trial-by-trial variations in the noise enveloppe influence phoneme categorization. Our results show that noise not only masks speech but also interacts with phonetic cues in systematic ways. This finding offers new insights into the hierarchical organization of phonetic cues and interindividual variability in speech perception.