Sibilants are characterized by the production of turbulent air- flow, which involves both a narrow constriction in the vocal tract and a certain volume velocity of the airflow. Despite both conditions being necessary for sibilant production, studies of constriction degree predominate in the literature. Using acous- tic and articulatory data, we show that in certain sequences Standard Mandarin apical vowels exhibit minimal lingual ad- justment compared to adjacent sibilants, while also exhibiting a considerable drop in frication noise. The same result was found for the vowel /i/. We hypothesize that the change in frication noise could be due to a number of different non-lingual factors and discuss the potential implications for models of sibilants.