This mixed-methods study investigated the impact of musical lyrics and working memory capacities on second language (L2) English reading comprehension among adult Chinese native speakers. Participants were 57 adult ESL learners with advanced L2 proficiency, divided into high and low working memory capacity groups based on a pre-test. They completed reading comprehension tasks while listening to the same melody with either Chinese or English lyrics. The results revealed that participants exhibited better reading comprehension, hence less distraction, when exposed to Chinese lyrics compared to English lyrics, contrary to initial expectations. Interestingly, working memory capacity did not significantly mediate the effects of background music on reading comprehension, suggesting that other factors such as linguistic familiarity and cognitive load may play a more prominent role. The interview data further highlighted participants' perceptions, indicating that music, particularly songs with lyrics in their native language, often distracts from reading tasks. This finding showed discrepancies between some adult learners' perception and their actual L2 reading performance. This study contributes to the understanding of how background music and its lyrics influence L2 reading and provides insights into the complex interplay between linguistic familiarity, cognitive resources, and reading performance.