Im having trouble with ruminating at the moment too. Over silly things for me, I get so caught up in the thoughts I dont realise what is going on in front of me. Im not good enough at mindfulness yet for that to work to stop the thoughts, and CBT, like you, only stops until I am not distracted again. For me it is more annoying than distressing, I can sometimes take a step back and watch the thoughts without letting them affect me too much.

Last night I tried redirecting the thoughts (since I cant stop the flow), everytime I would start to ruminate I would redirect the thoughts to think about something else (in my case some tv shows that I am watching). It worked for a bit but I had to keep redirecting the thoughts everytime they slipped back into rumination. I think I will keep trying this though because it would work for 10 mins or so at a time.