I'm just thinking out loud,我只是在自言自语。
A: Were you talking to me about something?
你和我说什么了吗？
B: No, I'm sorry. I was just thinking out loud.
没有，对不起。我刚才是在自言自语。

There's more to it than that.还有别的事情。/还有比那更深的含义。
A: I heard you quit your job because you were unhappy.
听说你因为不开心而辞职了。
B: There's more to it than that. I'll tell you about it later.
还有别的事情，我以后再和你说吧。