How do I repair a Radio turning itself on an off

My Fathers car, Purch new in 2003. Quite suddenly approx 5 months ago the radio started coming on and off, Not all the time. Somtimes it will work fine or not at all. Of course when it is cycling like that the antenna is moving up and down. Any ideas? The car is a creampuff and the radio has had minimal use. My Father asked Hyundai to repair it when he took it down for 15 K service, But they said his bumper to bumper part of warranty had expired. Nice huh, 90 yr old man with probably the lowest mile 2003 Sonata in excistence. Thanks Dave