On my Bose QC 25, a high-pitched intermittent squealing noise in the right headphone. It's hardly Quiet Comfort!! It is so loud and piercing it makes the headphones impossible to use unless I remove the batter (which removes the noise cancelling function of course). It only starts when I put the right headphone over my ear. However, I can also get it to make the noise when I remove the pad on the right side, and simply place my hand, or even just one finger, across the headphone without touching the perforated cover inside. It sounds to me just like a feedback squeal. I see similar problems reported for the QC 35, and the 700. Any suggestions about what's to be done. Because of the current Covid-19 crisis, Bose seems to have shut down its phone support here in Australia, and there's no online support either.
Thanks for reaching out. Welcome to the Community.
I'm sorry to hear you are having issues with your headphones. Squealing can sometimes occur if the outer microphone used for active noise cancellation comes into contact with the speakers inside the earcup. This could be due to the cushions being deteriorated or not fitted correctly. If they look worn, I would recommend replacing the cushions. If they look okay, I would recommend removing them from the headphones then re-attach them, then test to see if the squealing persists.
If the issue continues, please get in touch with local support to discuss service here.