Need Help

I agree with the last solution. Turn the plug around. This should eliminate any ground loop problems. Also, unplug any TVs to be sure. If there is still a hum, it needs serviced.

Whether switching power supply or linear (whichever it is) try this experiment. Disconnect all inputs to the receiver & retest. Also try turning the AC plug around & test once more. Also try it with the tuner playing. If you get a buzz no matter what, then the receiver's power supply needs repairing.

I had similar problems with a Sony RX that i took to a friends house for him to use. This model had one of their "fancy" pulse width ( or some funky name ) power supplies in it. No matter where we plugged it into in his house, it had a nasty buzz to it. Several other receivers worked fine though. Plugging the Sony into any outlets in my or anyone else's house did not present a problem. My guess is that this guy ( and your Father ) have got something wrong with their house wiring. Sean
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Sounds like a capacitor failing in the power supply. It may be arcing at its own frequency determined by the progress of its failure. It would be one of the types of failure that could affect both channels. I recommend taking it in to an authorized Sony electronics repair shop. Good luck!

Which model Sony receiver?

Is there a loud buzz with no CD changer connected and just the receiver turned on and set to FM? If so the problem is in the receiver.