Very helpful!
First of all, do you follow the recommendations of journaling which are designed to elicit a fully-honest and hopefully emotional result?
1. Don't let your TMS brain dictate what you do or don't write down
2. Absolutely do not edit what you're writing as it comes off the end of your pen or out of your keyboard. If you stop to edit, correct, make it legible, or phrase something differently so that it doesn't sound as bad or it's not as embarrassing or whatever, you've lost the essential honesty.
3. Throw out what you write as soon as you finish writing it.
Nicole Sachs says that it takes more than ten minutes of what I call "writing shit down" before the unconscious stuff starts showing itself. Read her web advice by doing a search for "Nicole Sachs JournalSpeak" and you'll find it.
Try starting a writing session by asking yourself a question in the third person (a technique recommended by Ethan Kross by the way). Such as "okay, JB, what is it about this earworm that bothers you so much? Is it the tune itself and what it says about me that it's this particular tune? What other thoughts is this connected with?" and just let the free thoughts flow, whatever stream of consciousness comes out, even if it's just conversational back and forth. The idea is to keep the words coming out without thinking about them, and of course absolutely not editing them.
Good luck.