Are you using any of the analog/digital outputs or only the audio outputs? Is it possible that this noise you hear is coming from the analog/digital outputs instead of the audio outputs? Have you tried this on a more recent Bela image? There has been some improvement since 5 years ago on what happens to the outputs when there is a dropout, so it may be worth a try. Regarding updating image, IIRC you were using a custom libpd render C++ file (or not?). If you were, then you may need some help to update it to the most recent version, I can help with that, just let me know.
