Drone note in audio, cannot remove

Hi all, this has been reported before a couple of times without resolution, but in the audio of my piece (for strings), as I play it or when exported, there is an incessant drone of a high note in the background, nowhere to be found in the score. I've reset core audio on my Macbook Pro, have reset MuseScore 4 prefs, restarted the app numerous times, but it's still there. I'm desperate not to have to rewrite the whole piece from scratch!

Can anyone help?

Thank you in advance.
David