I have a ten year old Samson Servo 120 amplifier that developed an faint intermittent crackling in the right channel a few months ago. Some days the crackling would be there, some days not. Recently, though, the crackling has gotten louder and more persistent, and now it seems to have spread to the left channel. The crackling only occurs when sound is run through the amplifier. I have checked the cables and the speakers because it originally sounded like I might have a loose connection or bad speaker. Yesterday, though, I verified that the amp seems to be the source of the problem. This amp has NOT been used hard; for a few years it was only turned on once or twice a week. Any theories on what sort of repairs might be needed? Thanks.