How is a speaker solid state?
If the speaker itself is going then it will usually make noises that sound like you have a few paperclips in it or something to that affect.
Try hooking the right speaker to where the left hooks up and the other way around, and see what happens. Cutting out is usually another problem, like loose connections, even cleaning the connections may help.
But like OuterSquare said age is a factor but not a very big one with speakers, I know several big house sets that have survived for over 20 years.