。
There's something I want to talk about...
Literal
Want-to-talk things [subject-が] exist [explanatory-のだ] [trailing-けど].
The trailing けど ('but...') leaves the sentence deliberately incomplete — a very common Japanese softening device for introducing a topic without being pushy. のだ adds explanatory nuance ('the thing is...'). The whole sentence gently signals 'I have something to say, if you're willing to listen.'