I had a weird buzz in my tenor uke that no normal investigation would pinpoint. We checked the termination points (pins and nut), looked for anything loose inside, eliminated the usual culprit of fret/string buzz, etc. I took off and repositioned the G string, thinking it might have a fault. Still no solution.
As I was repositioning that string and holding the head to the light, I noticed the key peg had a very tiny bit of light between the peg head and the metal stem....touching my fingertip to the head as I plucked the string, the buzz disappeared! Aha!
So I took off the string from the tuning mechanism, unscrewed the hardware, and VERY lightly tapped the key peg head onto the metal stem. With the gap gone, the buzz went away also.
It was such a tiny gap it would never have been noticed in the initial setup, and the buzz didn’t show up until several months after purchase of this uke.