According to the duplex mechanism, short-term memory can be disrupted by two functional distinct forms of auditory distraction. The presentation of acoustic deviants is associated with the diversion of attentional resources away from the focal task towards an irrelevant sound and it was found that the deviation effect is reduced in individuals with higher working memory capacity. On the other hand, the changing-state effect is supposed to be due to involuntary seriation processing of acoustical changes leading to interference with deliberate serial-order processing. The changing-state effect was found to be independent of individual working memory capacity. The present study investigates the causal effect of working memory capacity on auditory distraction. Therefore, participants’ working memory capacity was enhanced through an online cognitive training (n = 28) with eight sessions of an adaptive dual n-back task (requiring responses to visual and auditory targets n trials back). An active control group (n = 28) practiced a non-adaptive dual 0-back task online (eight sessions), requiring responses only to the current trials. Before and after the training, all participants conducted a serial recall task with different types of auditory distractors (e.g., changing-state speech, auditory deviants). Both groups showed comparable improvements in serial recall accuracy, but the working-memory training did not lead to a reliable reduction of auditory distraction. The results suggest that the diversion of attention through irrelevant sound may be less susceptible to cognitive control than previously thought.