If something gets stuck between the reed and its holder (frame), the reed may not vibrate at all, or will make a horrible buzzing noise instead of playing the desired note. Fixing this can be somewhat involved and requires gently scraping the edge of the reed or the reed frame. If it is not a constant problem, it can be helpful to me if you not only determine what key has the bad reed, but also whether it is the lower (bass) reeds or the upper (male) reeds. While playing the key with the bad reed, open the main (not drone) stops until you hear the buzzing (or don’t hear the dead note!) and make a note of it.