[Alan Brinton]

The reed might be slightly bent or twisted. If you examine the whole length of it, do you notice any difference in comparison with the other reeds? In particular, is there a difference in how it lines up with the reed plate near its base? It could be that the entire reed is not vibrating freely. You might try gently pushing the reed from the side to move it ever so slightly to the left or right. It could be catching on one side. I have done this using the side of a straight razor blade. It’s a tricky business, however. I’m sure you’ve already checked for any protrusion from the reed from scraping or debris around it.

Also, do you notice any difference in the key action for that note? Either in how the key presses and springs back or how the pad lever lifts to let air through? And is there any difference in the pad itself in comparison to the others? It’s surface or how it lines up?