Hum is in the sub and speakers -- I disconnected the G68 again and found the hum is present at faint levels without connection to the G68 which I would say is normal for a subwoofer. When I reconnected the G68, it was not as audible as before, although it was somewhat more audible than without connection to the G68. I think it is probably ok. What would I hear if there was a problem like a ground or earth loop?