Has any VTF-3 owners experienced a very slight hum when the amp is on (green light)? You have to get very close..about a foot away to hear it and it is not audible from the seating position. This is not a ground loop problem. Everything is plugged into a Monster 5000 line conditioner. Have tried cheater plug with no results. Is this normal for the VTF-3? I plugged another sub into the same outlet and hooked it up and it was dead quiet. The HSU people thought it could be a power supply prob????