I found this amp at a Goodwill and brought it home. After checking things out I found it has a hum when it is switched to the phono input. I thought it may have a bad cap some where, so I replaced all the electrolytic caps. Power up after cap install and the hum is still there and found another problem. When I touch the volume control (without the knob on) there is a buzz. Is there a small amount of voltage on the volume knob that is grounded when I touch it? Any help would be great!