Objective: Intrusive thoughts are characterized by a sense of intrusiveness of foreign entry into cognition. While not always consisting of negative content, intrusive thoughts are almost solely investigated in that context. Involuntary Musical Imagery (INMI) offers a promising alternative, as it is a type of involuntary cognition that can be used to evaluate intrusiveness without negative content. Methos: In Study 1, 200 participants completed self-report questionnaires to assess several aspects of intrusiveness: meta-awareness, control, repetitiveness, frequency, and subjective experience of INMI. In Study 2, 203 participants completed self-report questionnaires to explore the clinical characteristics (depression, stress, anxiety, and rumination) which might mediate the connection between INMI frequency and INMI negative experience. Results: Study 1 revealed, through exploratory factor analysis, that intrusiveness shares variance with the negative experience of INMI but not with INMI frequency. In study 2, ruminative thinking was found to mediate the relationship between frequent INMI and negative experience of INMI. Conclusion: These results suggest that INMI might be used to investigate intrusiveness in the lab without the potential confound of negative emotions. In addition, the results suggest that neither the content nor the frequency of intrusive thoughts can solely explain why these thoughts are aversive to some but not others. Ruminative style might be the missing link to explain how and why these intrusive thoughts become aversive and obsessive. In other words, we suggest that the cause for intrusiveness lies not in the thought or repetitiveness, but in the thinker.