Hi dj2fresh. Most likely you are noticing the hum from the step-down transformer on the back panel. While a faint hum is normal, it shouldn't be so loud that you can hear it across the room. Even with the power switch off the transformer is always receiving AC power when the cord is inserted and the plug is plugged in. This transformer steps the A/C voltage down to supply the dial light with low voltage AC power and lowers the voltage prior to the bridge rectifier to achieve the 15V DC power to the rest of the components.
I would like to add that this hum should not be present in the speakers with the unit switched off but may be noticeable through the speakers while switched on and the volume all the way down.
