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Marantz AV7702mkii hum issues?
If you hear a faint, or a loud, hum coming from the speakers connected to your Marantz preprocessor, here is the fix.
First step: ensure that the hum is present and playing through the speakers.
From this point on, you are going to disconnect each HDMI and analog input, while closely listening to the humming speaker. If the hum does not stop, then reconnect the disconnected connection.
When the humming stops, you have identified the issue — the source is the device you just disconnected.
Power off that device. Then disconnect the power of that device. Then connect a ground lifting adapter to its power plug. Then connect the ground lifter to the power socket.
That's it. The hum should be gone.
Enjoy!