Cracking channel on stereo?

I have a Craig 5501 amplifier that I found at the local swap shop at our recycling center. It initially worked great and sounded fantastic. But with time it developed a very loud crackling and popping in one channel. I tried swapping the speakers and it stayed on the same channel, so it's not the speakers. Is there a simple way to fix this or should I dump the thing back at the swap shop?