It is DC that is causing the pop and it's exhibited by some amps and not others. It's dependent on the amplifier design. This is information I recently received from Aragon tech support. I contacted them because my Acurus amp does not pop but my Aragon does. If there is DC present, the Aragon makes a small thump when changing inputs. The Acurus is a different design and doesn't. It's not harmful to the amp.