I can only speak from personal experience on that one, Nick.
When I write these words, what's going on in my mind is several flows of icons. The innermost ones are my own thoughts: the broad-stroke ideas and details I'm wanting to get across. Connected to that is a flow of iconics that would look somewhat like words to you, if you were reading them; but there's no 'voice' involved. Each 'word' icon is connected to one or more of my thought icons, and occasionally connected to thought-icons directly in the 'word' flow. Rarely - very, very rarely - the inner sight of a 'word'-icon triggers an aural memory of speech, but these memories lack meaning unless I concentrate on them and connect them to thought-icons.
Yes, my inner thoughts are utterly without sound. This could explain, in some way, why I work better with music playing constantly. Listening - as long as it's fairly passive - requires no shifting of focus in my mind regarding my thoughts. It cannot interrupt or drown out any 'inner dialogue' because, for me, the two are in seperate channels entirely.
I can't speak for others in similar situations, but that's my experience. In fact, it took me years to understand that other people DID 'talk in their heads'.
It also took me a while to learn writing, as it were, because it seemed such a cumbersome and tedious way to jot down thoughts.
Maybe this is why conscious experience is so different for the two of us. For me, every sensation has an icon flow associated with it, which I translate as 'thought'. But flows from each sense travel in different areas for me, unless I pull them into focus. That act - which I'm struggling to put into comprehensible terms - is more like the act of translating existing thoughts into a purer form for processing - stripping away spoken words, for example, to actually comprehend their meaning, rather than just blankly watching the words flow past.
If I gather correctly, what you term 'conscious thought' is what I might refer to as 'thought-icons' - the innermost layer of thinking, where it all comes together and processes (for those things that process within awareness). For you, it's a separate sensation from experiencing, because it has a different interior texture (although it's apparently one like hearing/speech). For me, it's the same as any other thought/experience, except that it resides in sharper focus at any given time and is easiest to understand.
Maybe I'm babbling - it's hard for me to say if I'm getting my point across.