Tracing down a small but annoying buzz (loose brace?)

Soprano ukulele I feel three braces in a fan design inside but I cant get my fingers in there and strum. Seems to have a buzz coming from the bridge area or inside the ukulele. I've already changed strings and raised the action using a small piece of paper under the string at the nut and saddle with little change.

Further experimentation and inspection looking for the saddle top possibly being too flat I notice all the strings create this buzz when plucked firmly and it seems to resonate most with the C string and all G's that I fret on other strings.

I dont know what else to do to try to eliminate anything else and verify a loose brace. I have a week before the seller is back from vacation so I was thinking of taking the strings off and pumping a g note at it through a speaker to see if it reproduces the buzz.

Then at least I could try getting my fingers in there to see.

Thoughts?

have you checked for hairline cracks

I thought I had my buzz narrowed down to a loose brace but now I question the nut. I noticed after changing the C string to a kala red concert string the buzz is almost gone. I noticed when I put my fingers in the sound hole to press on various braces I couldn't get the string to buzz plucking with my left hand. The further I strum or pick from the neck the more it buzzes leading me to believe it is the string itself. Further examination and I see what might be a crack in the bone nut and wonder if this is my whole issue in a nutshell.