When thinking more abstract or intense thoughts, for me it's probably more or less what you're describing? Sort of disembodied voice, at least when the focus is not on the qualities of the voice, but on the details of whatever the thought happens to be.

Although, I can also choose to listen to any thought in a voice of my choosing, if I focus on it. Then it has "real" voice qualities such as accent, pitch and tone, but without differing volume. And it always seems a bit duller than real voices. I guess that's how I would describe it at least.