As I've gotten older, my inner voice has been getting ever quieter, and now I often go long stretches without it. Like you, I sometimes feel like my inner critic has been saying something nasty, but mostly the thing has just shut up, which is very nice! At the same time I've gotten over my depression (never officially diagnosed, but I'm pretty sure I had it). Coincidence? I think not, but I don't know which is cause and which effect, or just how it happened, so I don't have any advice.
Related: Shoulder Advisors has a lot of practical advice as well as speculation on inner monologue, inner dialogue, and related phenomena in the post as well as comments.
This is something I've been puzzled by for a long time, for myself. The "inner critic" is generally described as a literal voice that people hear, saying things like "wow, I'm such an idiot", "nobody likes me", etc.
My problem here is that I generally don't think in words (except when thinking about how to explain something to others, like this), and I don't have thoughts that strongly resemble that kind of self-talk even in abstracted form. The closest thing I can identify to an inner critic is spontaneous emotional experiences that seem like they plausibly would be the emotional result I'd get if I had such a voice saying those kinds of things in my thoughts.
I've had some minor success with doing a combination of Focusing and journaling to try to put words to what I'm feeling, but it doesn't seem like it captures the same essence as all the writing about dealing with one's inner critic that I've found.
So for anyone else who is similarly nonverbal in their thinking: How do you experience your inner critic? Are there methods you have for identifying the thoughts, and interacting with them analogously to the typical verbal-oriented advice for dealing with one's inner critic?