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.
I think so too, but I guess it's relative: my younger sister suffers from the low-pitch/noisier variety, and she thinks having a constant high-pitch in your ear must be horrifying. She might be right, but I try not to think much about it.