Thanks for reaching out and welcome to the Bose Community Forums.
I am sorry that you are having issues with your QC3 headphones and would love to assist you.
To start with I would ensure that all of the cushions are securely attached to the headphones. After that I would try the following:
Be sure the screen covered earcup ports are not blocked. Blocked or covered earcup ports may cause squealing, feedback or other audio performance issues.
Ensure that the battery is fully charged.
Make sure the connected device is grounded. When connected to an ungrounded device, such as a computer or TV, it is possible for the headset to produce a humming sound. If possible, disconnect the device from power to eliminate this noise when listening, or find a grounded power outlet.
Remove the device from any case or protective sleeve. A case or sleeve may prevent the headphone connector from seating properly in the device. Removing the case will allow a proper connection.
If the above does not work, please can you try connecting a different audio device. Connecting to another audio device using the same cables and connections helps to determine if the issue is related to the first device or its settings.
I look forward to hearing back from you.
Vicky W - Community Support
Thank you for posting and welcome to the community. I'm sorry to hear you are also having this problem.
It is potentially possible for old ear cushions to cause this. If the ear cushions are not sitting securely against your ears, then it is possible to get feedback from the Noise Cancellation.
If you haven't already I would recommend trying the troubleshooting suggested by @Vicky_W above and seeing if that helps as well.