Everybody's does. There's a scientific reason for that, too.
Because my voice sounds different in my head, though, it's not much use for me to just listen back to prior recordings to see what I made different characters sound like (say, for a sequel).
Instead, I have to get back in touch with what attributes I had in mind with that character, that came through in their voice.
I love how this guy (exceptional at voices, all genders) has a "fleet of actors in his head" and he casts them in the roles that come in the books.
It's not like that for me.
I get the sound of a character by pinning some quality to them. Qualities like "Always expects the best of everyone", "aggressive to be taken seriously".
It's even better if I can boil it down to one word. Caffeinated. Skeptical. Serene. Snob. Tentative.
These cues almost always come out of the narrative. I pre-read the story, and just like everyone else reading a story, I get an imaginary vision of the characters. But in my case, I have to get the imaginary voice. Sometimes the author provides helpful character notes, but the story is most important.
Usually, it just starts the first few words that they speak. I can get a little bit in and be like, no no, that's all wrong for her, and start over. I can tell right away if I'm forcing a voice. Good writing gives good voices- voices fall on the characters and drape them completely.
To remember what I made a character sound like, I have to remember them, not their voice.