Wait a minute... I thought I had internal monologue because I can hear myself speaking thoughts and myself talking to myself (it's like talking out loud but in your head) but reading some of the comments here it seems like people have multiple inner voices and that's what they mean by internal monologue ? I don't have inner voices, there's only me up there (and I do a lot of self pitying and most of the monologue is…
Have you tried changing your inner voice to some one else's voice? I'm usually have 1 primary voice but I can synthesize anyone's voice. For example, if I'm reading something that I know was written by a woman my brain automatically makes up a female voice for it.
When reading fiction I have different tones for people but it's barely noticeable. I read without sub vocalizing much (reading too fast for that but I can pause it to enjoy the scene or the writing or the experience of reading, it depends).
I too make up voices for female and male authors of tweets, blog posts, articles, comments, etc. but it's automatic and they aren't discernable unless I have heard the person then it'll always be their voice.
And there's a huuuuuge bias because the default is a male voice with all of my stereotypes attached to it.