You may have another component on the same circuit or plugged into the same wall plug. (In my house, wall plugs on the same wall share a circuit). I recently introduced two subwoofers and two monoblocks into my system, and was getting a very faint hum as well. I went through the process of unplugging each component and putting my ear up to the midrange of my speakers to see if the hum was removed. Turned out that the culprit was the left subwoofer (and it’s class D amp introducing noise back into the line - that shared a wall plug with my preamp). I went to WalMart (high end audio store :D), and got a $2 pack of three ’cheater’ plugs that remove the ground, to use on my subwoofer. Hum disappeared. Note - probably NOT AUDIOPHILE APPROVED solution! You can do the same thing by floating the ground on your power cord (by snipping the ground pole on the plug if its a cheap cord, or by disassembling the plug and disconnecting the ground wire from the plug.) NOTE - I had no [audiophile ethical violation :)] problem putting a cheater plug on a subwoofer power cord; but others here with more electricity and component knowledge should chime in. These ’solutions’ may put your Viva Solista at some risk.
