try doing a search on hum and you'll see that it is most likely a ground loop - easily fixed.
Humming Noise
I have a pair of Don Cochran mono amps. One of them is causing the humming noise to speaker (B&W 801/3). I think one of the caps is leaking but not sure. How do I fix it? Don was out of business. Where do I send the unit for service? I have manual user and schematic. Please help. Thanks so lot in advance.