I have a mix of 75% no. "6" and 25% no. "9". It is loud enough that I can hear it while talking to people or walking on the street, but if I don't mind it or forget about it, I can go for days or months without hearing it. When I focus on it, it comes back shining.

Recently, I am trying to be mindful of my inner sound in a similar way to breath mindfulness.