There are a few things I would look for.
- Is there a light dimmer on the circuit or on a neighboring circuit? If so disconnect and see if problem stops.
- Are all your connections tight in the breaker box? They come loose with time and vibrate and cause noise. It was amazing the improvement I had after tightening all the screw terminals. (Eliminating hf microphonic vibration).
Do NOT bypass the ground with cheater plugs. This is a safety issue.
- Is there a light dimmer on the circuit or on a neighboring circuit? If so disconnect and see if problem stops.
- Are all your connections tight in the breaker box? They come loose with time and vibrate and cause noise. It was amazing the improvement I had after tightening all the screw terminals. (Eliminating hf microphonic vibration).
Do NOT bypass the ground with cheater plugs. This is a safety issue.