Try putting a cheater plug (a 3-prong to 2-prong adapter, leaving the safety ground prong unconnected) on all of the source components, simultaneously (but not on the amplifier). When you do that, try both connection polarities of each of the source component plugs.
If you don't have complete confidence in the integrity of the shield connections of the interconnects (for instance, if one of them may have been stepped on or tugged recently), try different interconnects.
If they are not already, try connecting the ac power plugs of the amplifier and the source components such that they are ALL connected to outlets on the power conditioner that are not isolated from each other in any way. Alternatively, remove the conditioner altogether and connect all power cords to the same duplex outlet or power strip.
If none of that helps, I would suspect unfortunately that the amplifier has an internal defect in its input switching circuit.
Hope that helps,
-- Al
If you don't have complete confidence in the integrity of the shield connections of the interconnects (for instance, if one of them may have been stepped on or tugged recently), try different interconnects.
If they are not already, try connecting the ac power plugs of the amplifier and the source components such that they are ALL connected to outlets on the power conditioner that are not isolated from each other in any way. Alternatively, remove the conditioner altogether and connect all power cords to the same duplex outlet or power strip.
If none of that helps, I would suspect unfortunately that the amplifier has an internal defect in its input switching circuit.
Hope that helps,
-- Al