I can’t fathom this out – have replaced the string, with a new 5th octave toggle and the problem perpetuates. 3rd B is in flat position – the neighboring A# doesn’t cause stuff elsewhere to buzz. The string’s okay in natural and sharp, but when I tune it between A to Bb it resonates & damn well sings like a mosquito – I didn’t think of doing anything to the button in the soundboard like emery paper/fibre and as it sounded so good when I replaced it last night, I cut the spare off. Huh. Help…….