Whatever you do, please DO NOT feel guilty or anything about such thoughts. Gee I don't even want to get started on how crazy my mind can act up sometimes. Ever since I was little I could create entire universes in my head. As I got older I noticed that my mind could literally go through sythesiesic patterns combining up to 50 associations at one time! It was undescibable, I mean you name it killing people, violent thoughts, perverse things, musical arrangements, conversations, excerpts from movies, loved ones turning into demons. And the funny thing is, this was all just crapp that my other than conscious mind had picked up throughout my life from numerous sources and in turn combined together to create big ugly "mind collages" as I call them, constantly changing as well. Having an explosive creative mind can be tough! If it's not directed properly(or dissolved). Usually these are arbitrary associations that sometimes have "Real" meanings. Usually the meanings are indirect. It could be that your forcing your thougthts, you can easily take any fleeting thougtht, give it some resistance, and it will soon turn into an annoying broken record.
Also remember that pent up emotions can be like "thought power plants" constantly pushing irrating thoughts up to consciousness. Try letting go of (sedona method works wonders, also Emoclear.com has wonderful processes, Drop into Essence is an version of Sedona on the Emoclear sight.) of your generalized pent up feelings. Then if you see that there are a few particular events or people that your emotions are attached to try letting go of that. Please though don't try to analyze your thoughts, they're like fluid constant flowing water. Let out some of those emotions and you'll find your mind quiets, then your meditations can help you deepen that quietness even more. You are not your thoughts, especially those repetive broken record ones. As much as my mind has exploded in both good and bad ways I find that when I let out my accumulated emotions that my explosions are good and that I can direct them as well. Take care.