The radio in my 2004

Question

the radio in my 2004 Mitsubishi Diamante does not work all the time if its off it has a high pitches wine ill turn it on and a big pop sound and no music but the next time i turn on my car the radio works it didnt have any sound for a long time we took it to a stero store and they said it sounds like the amp was blown so thats what we thought it was but since it works now part of the time im thinking its something else.