Did you have any power outages or surges?
Was there a lightning storm in your area?
If anything like the possible problems above occurred then the power supply circuitry may be damaged.
Or the power supply filter caps may be drying out, this would cause excessive AC ripple into the main circuitry.
To see if this is the problem the unit must be opened up, and the caps in the power supply circuit need to be inspected.
If any of the electrolytic caps that look like little metal cans have a bulged up top or a split top then the power supply circuit needs to be repaired or replaced.
Here is a photo to help you look over the caps in question.
Have you tried un-plugging the set from the AC power source for about ten min or so and see what happens?