Problem: The 20-22 "fret" area on my MTD Kingston Fretless 5 (24 frets) buzzes out on all strings. Any note played in that area just clicks, yet all notes are fine before and after that area. No excessive wear on fretboard. Used a ruler to test for flatness of board. No noticeable deviation from flatness. Tried raising strings at bridge, g string significantly, and problem persisted. Any suggestions?